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  <header>
    <aside>November 25, 2020</aside>
    <a href="https://gto76.github.io" rel="author">Jure Šorn</a>
  </header>

  <a href="javascript:" id="return-to-top"><i class="icon-chevron-up"></i></a>
   <div><h1 id="comprehensivepythoncheatsheet">Comprehensive Python Cheatsheet</h1><p class="banner"><sup><a href="https://raw.githubusercontent.com/gto76/python-cheatsheet/master/README.md">Download text file</a>, <a href="https://transactions.sendowl.com/products/78175486/4422834F/view">Buy PDF</a>, <a href="https://github.com/gto76/python-cheatsheet">Fork me on GitHub</a> or <a href="https://github.com/gto76/python-cheatsheet/wiki/Frequently-Asked-Questions">Check out FAQ</a>.
</sup></p><p class="banner"><img src="web/image_888.jpeg" alt="Monty Python"></p><br><div><h2 id="toc"><a href="#toc" name="toc">#</a>Contents</h2><pre><code class="hljs bash"><strong>ToC</strong> = {
    <strong><span class="hljs-string"><span class="hljs-string">'1. Collections'</span></span></strong>: [<a href="#list">List</a>, <a href="#dictionary">Dictionary</a>, <a href="#set">Set</a>, <a href="#tuple">Tuple</a>, <a href="#range">Range</a>, <a href="#enumerate">Enumerate</a>, <a href="#iterator">Iterator</a>, <a href="#generator">Generator</a>],
    <strong><span class="hljs-string"><span class="hljs-string">'2. Types'</span></span></strong>:       [<a href="#type">Type</a>, <a href="#string">String</a>, <a href="#regex">Regular_Exp</a>, <a href="#format">Format</a>, <a href="#numbers">Numbers</a>, <a href="#combinatorics">Combinatorics</a>, <a href="#datetime">Datetime</a>],
    <strong><span class="hljs-string"><span class="hljs-string">'3. Syntax'</span></span></strong>:      [<a href="#arguments">Args</a>, <a href="#inline">Inline</a>, <a href="#closure">Closure</a>, <a href="#decorator">Decorator</a>, <a href="#class">Class</a>, <a href="#ducktypes">Duck_Type</a>, <a href="#enum">Enum</a>, <a href="#exceptions">Exception</a>],
    <strong><span class="hljs-string"><span class="hljs-string">'4. System'</span></span></strong>:      [<a href="#exit">Exit</a>, <a href="#print">Print</a>, <a href="#input">Input</a>, <a href="#commandlinearguments">Command_Line_Arguments</a>, <a href="#open">Open</a>, <a href="#path">Path</a>, <a href="#oscommands">OS_Commands</a>],
    <strong><span class="hljs-string"><span class="hljs-string">'5. Data'</span></span></strong>:        [<a href="#json">JSON</a>, <a href="#pickle">Pickle</a>, <a href="#csv">CSV</a>, <a href="#sqlite">SQLite</a>, <a href="#bytes">Bytes</a>, <a href="#struct">Struct</a>, <a href="#array">Array</a>, <a href="#memoryview">Memory_View</a>, <a href="#deque">Deque</a>],
    <strong><span class="hljs-string"><span class="hljs-string">'6. Advanced'</span></span></strong>:    [<a href="#threading">Threading</a>, <a href="#operator">Operator</a>, <a href="#introspection">Introspection</a>, <a href="#metaprograming">Metaprograming</a>, <a href="#eval">Eval</a>, <a href="#coroutines">Coroutine</a>],
    <strong><span class="hljs-string"><span class="hljs-string">'7. Libraries'</span></span></strong>:   [<a href="#progressbar">Progress_Bar</a>, <a href="#plot">Plot</a>, <a href="#table">Table</a>, <a href="#curses">Curses</a>, <a href="#logging">Logging</a>, <a href="#scraping">Scraping</a>, <a href="#web">Web</a>, <a href="#profiling">Profile</a>,
                       <a href="#numpy">NumPy</a>, <a href="#image">Image</a>, <a href="#audio">Audio</a>, <a href="#pygame">Games</a>, <a href="#pandas">Data</a>, <a href="#pysimplegui">GUI</a>]
}
</code></pre></div></div>






<div><h2 id="main"><a href="#main" name="main">#</a>Main</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span>:     <span class="hljs-comment"># Runs main() if file wasn't imported.</span>
    main()
</code></pre></div>

<div><h2 id="list"><a href="#list" name="list">#</a>List</h2><pre><code class="python language-python hljs">&lt;list&gt; = &lt;list&gt;[from_inclusive : to_exclusive : ±step_size]
</code></pre></div>

<pre><code class="python language-python hljs">&lt;list&gt;.append(&lt;el&gt;)            <span class="hljs-comment"># Or: &lt;list&gt; += [&lt;el&gt;]</span>
&lt;list&gt;.extend(&lt;collection&gt;)    <span class="hljs-comment"># Or: &lt;list&gt; += &lt;collection&gt;</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;list&gt;.sort()
&lt;list&gt;.reverse()
&lt;list&gt; = sorted(&lt;collection&gt;)
&lt;iter&gt; = reversed(&lt;list&gt;)
</code></pre>
<pre><code class="python language-python hljs">sum_of_elements  = sum(&lt;collection&gt;)
elementwise_sum  = [sum(pair) <span class="hljs-keyword">for</span> pair <span class="hljs-keyword">in</span> zip(list_a, list_b)]
sorted_by_second = sorted(&lt;collection&gt;, key=<span class="hljs-keyword">lambda</span> el: el[<span class="hljs-number">1</span>])
sorted_by_both   = sorted(&lt;collection&gt;, key=<span class="hljs-keyword">lambda</span> el: (el[<span class="hljs-number">1</span>], el[<span class="hljs-number">0</span>]))
flatter_list     = list(itertools.chain.from_iterable(&lt;list&gt;))
product_of_elems = functools.reduce(<span class="hljs-keyword">lambda</span> out, el: out * el, &lt;collection&gt;)
list_of_chars    = list(&lt;str&gt;)
</code></pre>
<ul>
<li><strong>Module <a href="#operator">operator</a> provides functions itemgetter() and mul() that offer the same functionality as <a href="#lambda">lambda</a> expressions above.</strong></li>
</ul>
<pre><code class="python language-python hljs">&lt;int&gt; = &lt;list&gt;.count(&lt;el&gt;)     <span class="hljs-comment"># Returns number of occurrences. Also works on strings.</span>
index = &lt;list&gt;.index(&lt;el&gt;)     <span class="hljs-comment"># Returns index of first occurrence or raises ValueError.</span>
&lt;list&gt;.insert(index, &lt;el&gt;)     <span class="hljs-comment"># Inserts item at index and moves the rest to the right.</span>
&lt;el&gt; = &lt;list&gt;.pop([index])     <span class="hljs-comment"># Removes and returns item at index or from the end.</span>
&lt;list&gt;.remove(&lt;el&gt;)            <span class="hljs-comment"># Removes first occurrence of item or raises ValueError.</span>
&lt;list&gt;.clear()                 <span class="hljs-comment"># Removes all items. Also works on dictionary and set.</span>
</code></pre>
<div><h2 id="dictionary"><a href="#dictionary" name="dictionary">#</a>Dictionary</h2><pre><code class="python language-python hljs">&lt;view&gt; = &lt;dict&gt;.keys()                          <span class="hljs-comment"># Coll. of keys that reflects changes.</span>
&lt;view&gt; = &lt;dict&gt;.values()                        <span class="hljs-comment"># Coll. of values that reflects changes.</span>
&lt;view&gt; = &lt;dict&gt;.items()                         <span class="hljs-comment"># Coll. of key-value tuples that reflects chgs.</span>
</code></pre></div>

<pre><code class="python language-python hljs">value  = &lt;dict&gt;.get(key, default=<span class="hljs-keyword">None</span>)          <span class="hljs-comment"># Returns default if key is missing.</span>
value  = &lt;dict&gt;.setdefault(key, default=<span class="hljs-keyword">None</span>)   <span class="hljs-comment"># Returns and writes default if key is missing.</span>
&lt;dict&gt; = collections.defaultdict(&lt;type&gt;)        <span class="hljs-comment"># Creates a dict with default value of type.</span>
&lt;dict&gt; = collections.defaultdict(<span class="hljs-keyword">lambda</span>: <span class="hljs-number">1</span>)     <span class="hljs-comment"># Creates a dict with default value 1.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;dict&gt; = dict(&lt;collection&gt;)                     <span class="hljs-comment"># Creates a dict from coll. of key-value pairs.</span>
&lt;dict&gt; = dict(zip(keys, values))                <span class="hljs-comment"># Creates a dict from two collections.</span>
&lt;dict&gt; = dict.fromkeys(keys [, value])          <span class="hljs-comment"># Creates a dict from collection of keys.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;dict&gt;.update(&lt;dict&gt;)                           <span class="hljs-comment"># Adds items. Replaces ones with matching keys.</span>
value = &lt;dict&gt;.pop(key)                         <span class="hljs-comment"># Removes item or raises KeyError.</span>
{k <span class="hljs-keyword">for</span> k, v <span class="hljs-keyword">in</span> &lt;dict&gt;.items() <span class="hljs-keyword">if</span> v == value}    <span class="hljs-comment"># Returns set of keys that point to the value.</span>
{k: v <span class="hljs-keyword">for</span> k, v <span class="hljs-keyword">in</span> &lt;dict&gt;.items() <span class="hljs-keyword">if</span> k <span class="hljs-keyword">in</span> keys}  <span class="hljs-comment"># Returns a dictionary, filtered by keys.</span>
</code></pre>
<div><h3 id="counter">Counter</h3><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> Counter
<span class="hljs-meta">&gt;&gt;&gt; </span>colors = [<span class="hljs-string">'blue'</span>, <span class="hljs-string">'blue'</span>, <span class="hljs-string">'blue'</span>, <span class="hljs-string">'red'</span>, <span class="hljs-string">'red'</span>]
<span class="hljs-meta">&gt;&gt;&gt; </span>counter = Counter(colors)
<span class="hljs-meta">&gt;&gt;&gt; </span>counter[<span class="hljs-string">'yellow'</span>] += <span class="hljs-number">1</span>
Counter({<span class="hljs-string">'blue'</span>: <span class="hljs-number">3</span>, <span class="hljs-string">'red'</span>: <span class="hljs-number">2</span>, <span class="hljs-string">'yellow'</span>: <span class="hljs-number">1</span>})
<span class="hljs-meta">&gt;&gt;&gt; </span>counter.most_common()[<span class="hljs-number">0</span>]
(<span class="hljs-string">'blue'</span>, <span class="hljs-number">3</span>)
</code></pre></div>

<div><h2 id="set"><a href="#set" name="set">#</a>Set</h2><pre><code class="python language-python hljs">&lt;set&gt; = set()
</code></pre></div>

<pre><code class="python language-python hljs">&lt;set&gt;.add(&lt;el&gt;)                                 <span class="hljs-comment"># Or: &lt;set&gt; |= {&lt;el&gt;}</span>
&lt;set&gt;.update(&lt;collection&gt; [, ...])              <span class="hljs-comment"># Or: &lt;set&gt; |= &lt;set&gt;</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;set&gt;  = &lt;set&gt;.union(&lt;coll.&gt;)                   <span class="hljs-comment"># Or: &lt;set&gt; | &lt;set&gt;</span>
&lt;set&gt;  = &lt;set&gt;.intersection(&lt;coll.&gt;)            <span class="hljs-comment"># Or: &lt;set&gt; &amp; &lt;set&gt;</span>
&lt;set&gt;  = &lt;set&gt;.difference(&lt;coll.&gt;)              <span class="hljs-comment"># Or: &lt;set&gt; - &lt;set&gt;</span>
&lt;set&gt;  = &lt;set&gt;.symmetric_difference(&lt;coll.&gt;)    <span class="hljs-comment"># Or: &lt;set&gt; ^ &lt;set&gt;</span>
&lt;bool&gt; = &lt;set&gt;.issubset(&lt;coll.&gt;)                <span class="hljs-comment"># Or: &lt;set&gt; &lt;= &lt;set&gt;</span>
&lt;bool&gt; = &lt;set&gt;.issuperset(&lt;coll.&gt;)              <span class="hljs-comment"># Or: &lt;set&gt; &gt;= &lt;set&gt;</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;el&gt; = &lt;set&gt;.pop()                              <span class="hljs-comment"># Raises KeyError if empty.</span>
&lt;set&gt;.remove(&lt;el&gt;)                              <span class="hljs-comment"># Raises KeyError if missing.</span>
&lt;set&gt;.discard(&lt;el&gt;)                             <span class="hljs-comment"># Doesn't raise an error.</span>
</code></pre>
<div><h3 id="frozenset">Frozen Set</h3><ul>
<li><strong>Is immutable and hashable.</strong></li>
<li><strong>That means it can be used as a key in a dictionary or as an element in a set.</strong></li>
</ul><pre><code class="python language-python hljs">&lt;frozenset&gt; = frozenset(&lt;collection&gt;)
</code></pre></div>


<div><h2 id="tuple"><a href="#tuple" name="tuple">#</a>Tuple</h2><p><strong>Tuple is an immutable and hashable list.</strong></p><pre><code class="python language-python hljs">&lt;tuple&gt; = ()
&lt;tuple&gt; = (&lt;el&gt;, )
&lt;tuple&gt; = (&lt;el_1&gt;, &lt;el_2&gt; [, ...])
</code></pre></div>


<div><h3 id="namedtuple">Named Tuple</h3><p><strong>Tuple's subclass with named elements.</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> namedtuple
<span class="hljs-meta">&gt;&gt;&gt; </span>Point = namedtuple(<span class="hljs-string">'Point'</span>, <span class="hljs-string">'x y'</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>p = Point(<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>)
Point(x=<span class="hljs-number">1</span>, y=<span class="hljs-number">2</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>p[<span class="hljs-number">0</span>]
<span class="hljs-number">1</span>
<span class="hljs-meta">&gt;&gt;&gt; </span>p.x
<span class="hljs-number">1</span>
<span class="hljs-meta">&gt;&gt;&gt; </span>getattr(p, <span class="hljs-string">'y'</span>)
<span class="hljs-number">2</span>
<span class="hljs-meta">&gt;&gt;&gt; </span>p._fields  <span class="hljs-comment"># Or: Point._fields</span>
(<span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>)
</code></pre></div>


<div><h2 id="range"><a href="#range" name="range">#</a>Range</h2><pre><code class="python language-python hljs">&lt;range&gt; = range(to_exclusive)
&lt;range&gt; = range(from_inclusive, to_exclusive)
&lt;range&gt; = range(from_inclusive, to_exclusive, ±step_size)
</code></pre></div>

<pre><code class="python language-python hljs">from_inclusive = &lt;range&gt;.start
to_exclusive   = &lt;range&gt;.stop
</code></pre>
<div><h2 id="enumerate"><a href="#enumerate" name="enumerate">#</a>Enumerate</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">for</span> i, el <span class="hljs-keyword">in</span> enumerate(&lt;collection&gt; [, i_start]):
    ...
</code></pre></div>

<div><h2 id="iterator"><a href="#iterator" name="iterator">#</a>Iterator</h2><pre><code class="python language-python hljs">&lt;iter&gt; = iter(&lt;collection&gt;)                 <span class="hljs-comment"># `iter(&lt;iter&gt;)` returns unmodified iterator.</span>
&lt;iter&gt; = iter(&lt;function&gt;, to_exclusive)     <span class="hljs-comment"># A sequence of return values until 'to_exclusive'.</span>
&lt;el&gt;   = next(&lt;iter&gt; [, default])           <span class="hljs-comment"># Raises StopIteration or returns 'default' on end.</span>
&lt;list&gt; = list(&lt;iter&gt;)                       <span class="hljs-comment"># Returns a list of iterator's remaining elements.</span>
</code></pre></div>

<div><h3 id="itertools">Itertools</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> itertools <span class="hljs-keyword">import</span> count, repeat, cycle, chain, islice
</code></pre></div>

<pre><code class="python language-python hljs">&lt;iter&gt; = count(start=<span class="hljs-number">0</span>, step=<span class="hljs-number">1</span>)             <span class="hljs-comment"># Returns updated value endlessly. Accepts floats.</span>
&lt;iter&gt; = repeat(&lt;el&gt; [, times])             <span class="hljs-comment"># Returns element endlessly or 'times' times.</span>
&lt;iter&gt; = cycle(&lt;collection&gt;)                <span class="hljs-comment"># Repeats the sequence endlessly.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;iter&gt; = chain(&lt;coll_1&gt;, &lt;coll_2&gt; [, ...])  <span class="hljs-comment"># Empties collections in order.</span>
&lt;iter&gt; = chain.from_iterable(&lt;collection&gt;)  <span class="hljs-comment"># Empties collections inside a collection in order.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;iter&gt; = islice(&lt;coll&gt;, to_exclusive)       <span class="hljs-comment"># Only returns first 'to_exclusive' elements.</span>
&lt;iter&gt; = islice(&lt;coll&gt;, from_inclusive, …)  <span class="hljs-comment"># `to_exclusive, step_size`.</span>
</code></pre>
<div><h2 id="generator"><a href="#generator" name="generator">#</a>Generator</h2><ul>
<li><strong>Any function that contains a yield statement returns a generator.</strong></li>
<li><strong>Generators and iterators are interchangeable.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">count</span><span class="hljs-params">(start, step)</span>:</span>
    <span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
        <span class="hljs-keyword">yield</span> start
        start += step
</code></pre></div>


<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>counter = count(<span class="hljs-number">10</span>, <span class="hljs-number">2</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>next(counter), next(counter), next(counter)
(<span class="hljs-number">10</span>, <span class="hljs-number">12</span>, <span class="hljs-number">14</span>)
</code></pre>
<div><h2 id="type"><a href="#type" name="type">#</a>Type</h2><ul>
<li><strong>Everything is an object.</strong></li>
<li><strong>Every object has a type.</strong></li>
<li><strong>Type and class are synonymous.</strong></li>
</ul><pre><code class="python language-python hljs">&lt;type&gt; = type(&lt;el&gt;)                          <span class="hljs-comment"># Or: &lt;el&gt;.__class__</span>
&lt;bool&gt; = isinstance(&lt;el&gt;, &lt;type&gt;)            <span class="hljs-comment"># Or: issubclass(type(&lt;el&gt;), &lt;type&gt;)</span>
</code></pre></div>


<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>type(<span class="hljs-string">'a'</span>), <span class="hljs-string">'a'</span>.__class__, str
(&lt;<span class="hljs-class"><span class="hljs-title">class</span> '<span class="hljs-title">str</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">str</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">str</span>'&gt;)
</span></code></pre>
<div><h4 id="sometypesdonothavebuiltinnamessotheymustbeimported">Some types do not have built-in names, so they must be imported:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> types <span class="hljs-keyword">import</span> FunctionType, MethodType, LambdaType, GeneratorType
</code></pre></div>

<div><h3 id="abstractbaseclasses">Abstract Base Classes</h3><p><strong>Each abstract base class specifies a set of virtual subclasses. These classes are then recognized by isinstance() and issubclass() as subclasses of the ABC, although they are really not. ABC can also manually decide whether or not a specific class is its virtual subclass, usually based on which methods the class has implemented (Collection, Iterable).</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> collections.abc <span class="hljs-keyword">import</span> Sequence, Collection, Iterable
<span class="hljs-meta">&gt;&gt;&gt; </span>isinstance([<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>], Iterable)
<span class="hljs-keyword">True</span>
</code></pre></div>


<pre><code class="text language-text">┏━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┓
┃                  │  Sequence  │ Collection │  Iterable  ┃
┠──────────────────┼────────────┼────────────┼────────────┨
┃ list, range, str │     ✓      │     ✓      │     ✓      ┃
┃ dict, set        │            │     ✓      │     ✓      ┃
┃ iter             │            │            │     ✓      ┃
┗━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┛
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> numbers <span class="hljs-keyword">import</span> Integral, Rational, Real, Complex, Number
<span class="hljs-meta">&gt;&gt;&gt; </span>isinstance(<span class="hljs-number">123</span>, Number)
<span class="hljs-keyword">True</span>
</code></pre>
<pre><code class="text language-text">┏━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┓
┃                    │ Integral │ Rational │   Real   │ Complex  │  Number  ┃
┠────────────────────┼──────────┼──────────┼──────────┼──────────┼──────────┨
┃ int                │    ✓     │    ✓     │    ✓     │    ✓     │    ✓     ┃
┃ fractions.Fraction │          │    ✓     │    ✓     │    ✓     │    ✓     ┃
┃ float              │          │          │    ✓     │    ✓     │    ✓     ┃
┃ complex            │          │          │          │    ✓     │    ✓     ┃
┃ decimal.Decimal    │          │          │          │          │    ✓     ┃
┗━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┛
</code></pre>
<div><h2 id="string"><a href="#string" name="string">#</a>String</h2><pre><code class="python language-python hljs">&lt;str&gt;  = &lt;str&gt;.strip()                       <span class="hljs-comment"># Strips all whitespace characters from both ends.</span>
&lt;str&gt;  = &lt;str&gt;.strip(<span class="hljs-string">'&lt;chars&gt;'</span>)              <span class="hljs-comment"># Strips all passed characters from both ends.</span>
</code></pre></div>

<pre><code class="python language-python hljs">&lt;list&gt; = &lt;str&gt;.split()                       <span class="hljs-comment"># Splits on one or more whitespace characters.</span>
&lt;list&gt; = &lt;str&gt;.split(sep=<span class="hljs-keyword">None</span>, maxsplit=<span class="hljs-number">-1</span>)  <span class="hljs-comment"># Splits on 'sep' str at most 'maxsplit' times.</span>
&lt;list&gt; = &lt;str&gt;.splitlines(keepends=<span class="hljs-keyword">False</span>)    <span class="hljs-comment"># Splits on \n,\r,\r\n. Keeps them if 'keepends'.</span>
&lt;str&gt;  = &lt;str&gt;.join(&lt;coll_of_strings&gt;)       <span class="hljs-comment"># Joins elements using string as separator.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;bool&gt; = &lt;sub_str&gt; <span class="hljs-keyword">in</span> &lt;str&gt;                  <span class="hljs-comment"># Checks if string contains a substring.</span>
&lt;bool&gt; = &lt;str&gt;.startswith(&lt;sub_str&gt;)         <span class="hljs-comment"># Pass tuple of strings for multiple options.</span>
&lt;bool&gt; = &lt;str&gt;.endswith(&lt;sub_str&gt;)           <span class="hljs-comment"># Pass tuple of strings for multiple options.</span>
&lt;int&gt;  = &lt;str&gt;.find(&lt;sub_str&gt;)               <span class="hljs-comment"># Returns start index of first match or -1.</span>
&lt;int&gt;  = &lt;str&gt;.index(&lt;sub_str&gt;)              <span class="hljs-comment"># Same but raises ValueError if missing.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;str&gt;  = &lt;str&gt;.replace(old, new [, count])   <span class="hljs-comment"># Replaces 'old' with 'new' at most 'count' times.</span>
&lt;str&gt;  = &lt;str&gt;.translate(&lt;table&gt;)            <span class="hljs-comment"># Use `str.maketrans(&lt;dict&gt;)` to generate table.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;str&gt;  = chr(&lt;int&gt;)                          <span class="hljs-comment"># Converts int to Unicode char.</span>
&lt;int&gt;  = ord(&lt;str&gt;)                          <span class="hljs-comment"># Converts Unicode char to int.</span>
</code></pre>
<ul>
<li><strong>Also: <code class="python hljs"><span class="hljs-string">'lstrip()'</span></code>, <code class="python hljs"><span class="hljs-string">'rstrip()'</span></code>.</strong></li>
<li><strong>Also: <code class="python hljs"><span class="hljs-string">'lower()'</span></code>, <code class="python hljs"><span class="hljs-string">'upper()'</span></code>, <code class="python hljs"><span class="hljs-string">'capitalize()'</span></code> and <code class="python hljs"><span class="hljs-string">'title()'</span></code>.</strong></li>
</ul>
<div><h3 id="propertymethods">Property Methods</h3><pre><code class="text language-text">┏━━━━━━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┯━━━━━━━━━━┓
┃               │ [ !#$%…] │ [a-zA-Z] │  [¼½¾]   │  [²³¹]   │  [0-9]   ┃
┠───────────────┼──────────┼──────────┼──────────┼──────────┼──────────┨
┃ isprintable() │    ✓     │    ✓     │    ✓     │    ✓     │    ✓     ┃
┃ isalnum()     │          │    ✓     │    ✓     │    ✓     │    ✓     ┃
┃ isnumeric()   │          │          │    ✓     │    ✓     │    ✓     ┃
┃ isdigit()     │          │          │          │    ✓     │    ✓     ┃
┃ isdecimal()   │          │          │          │          │    ✓     ┃
┗━━━━━━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┷━━━━━━━━━━┛
</code></pre></div>

<ul>
<li><strong>Also: <code class="python hljs"><span class="hljs-string">'isspace()'</span></code> checks for <code class="python hljs"><span class="hljs-string">'[ \t\n\r\f\v…]'</span></code>.</strong></li>
</ul>
<div><h2 id="regex"><a href="#regex" name="regex">#</a>Regex</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> re
&lt;str&gt;   = re.sub(&lt;regex&gt;, new, text, count=<span class="hljs-number">0</span>)  <span class="hljs-comment"># Substitutes all occurrences with 'new'.</span>
&lt;list&gt;  = re.findall(&lt;regex&gt;, text)            <span class="hljs-comment"># Returns all occurrences as strings.</span>
&lt;list&gt;  = re.split(&lt;regex&gt;, text, maxsplit=<span class="hljs-number">0</span>)  <span class="hljs-comment"># Use brackets in regex to include the matches.</span>
&lt;Match&gt; = re.search(&lt;regex&gt;, text)             <span class="hljs-comment"># Searches for first occurrence of the pattern.</span>
&lt;Match&gt; = re.match(&lt;regex&gt;, text)              <span class="hljs-comment"># Searches only at the beginning of the text.</span>
&lt;iter&gt;  = re.finditer(&lt;regex&gt;, text)           <span class="hljs-comment"># Returns all occurrences as match objects.</span>
</code></pre></div>

<ul>
<li><strong>Search() and match() return None if they can't find a match.</strong></li>
<li><strong>Argument <code class="python hljs"><span class="hljs-string">'flags=re.IGNORECASE'</span></code> can be used with all functions.</strong></li>
<li><strong>Argument <code class="python hljs"><span class="hljs-string">'flags=re.MULTILINE'</span></code> makes <code class="python hljs"><span class="hljs-string">'^'</span></code> and <code class="python hljs"><span class="hljs-string">'$'</span></code> match the start/end of each line.</strong></li>
<li><strong>Argument <code class="python hljs"><span class="hljs-string">'flags=re.DOTALL'</span></code> makes dot also accept the <code class="python hljs"><span class="hljs-string">'\n'</span></code>.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">r'\1'</span></code> or <code class="python hljs"><span class="hljs-string">'\\1'</span></code> for backreference.</strong></li>
<li><strong>Add <code class="python hljs"><span class="hljs-string">'?'</span></code> after an operator to make it non-greedy.</strong></li>
</ul>
<div><h3 id="matchobject">Match Object</h3><pre><code class="python language-python hljs">&lt;str&gt;   = &lt;Match&gt;.group()                      <span class="hljs-comment"># Returns the whole match. Also group(0).</span>
&lt;str&gt;   = &lt;Match&gt;.group(<span class="hljs-number">1</span>)                     <span class="hljs-comment"># Returns part in the first bracket.</span>
&lt;tuple&gt; = &lt;Match&gt;.groups()                     <span class="hljs-comment"># Returns all bracketed parts.</span>
&lt;int&gt;   = &lt;Match&gt;.start()                      <span class="hljs-comment"># Returns start index of the match.</span>
&lt;int&gt;   = &lt;Match&gt;.end()                        <span class="hljs-comment"># Returns exclusive end index of the match.</span>
</code></pre></div>

<div><h3 id="specialsequences">Special Sequences</h3><ul>
<li><strong>By default digits, alphanumerics and whitespaces from all alphabets are matched, unless <code class="python hljs"><span class="hljs-string">'flags=re.ASCII'</span></code> argument is used.</strong></li>
<li><strong>Use a capital letter for negation.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-string">'\d'</span> == <span class="hljs-string">'[0-9]'</span>                                <span class="hljs-comment"># Matches any digit.</span>
<span class="hljs-string">'\w'</span> == <span class="hljs-string">'[a-zA-Z0-9_]'</span>                         <span class="hljs-comment"># Matches any alphanumeric.</span>
<span class="hljs-string">'\s'</span> == <span class="hljs-string">'[ \t\n\r\f\v]'</span>                        <span class="hljs-comment"># Matches any whitespace.</span>
</code></pre></div>


<div><h2 id="format"><a href="#format" name="format">#</a>Format</h2><pre><code class="python language-python hljs">&lt;str&gt; = <span class="hljs-string">f'<span class="hljs-subst">{&lt;el_1&gt;}</span>, <span class="hljs-subst">{&lt;el_2&gt;}</span>'</span>
&lt;str&gt; = <span class="hljs-string">'{}, {}'</span>.format(&lt;el_1&gt;, &lt;el_2&gt;)
</code></pre></div>

<div><h3 id="attributes">Attributes</h3><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> namedtuple
<span class="hljs-meta">&gt;&gt;&gt; </span>Person = namedtuple(<span class="hljs-string">'Person'</span>, <span class="hljs-string">'name height'</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>person = Person(<span class="hljs-string">'Jean-Luc'</span>, <span class="hljs-number">187</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-string">f'<span class="hljs-subst">{person.height}</span>'</span>
<span class="hljs-string">'187'</span>
<span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-string">'{p.height}'</span>.format(p=person)
<span class="hljs-string">'187'</span>
</code></pre></div>

<div><h3 id="generaloptions">General Options</h3><pre><code class="python language-python hljs">{&lt;el&gt;:&lt;<span class="hljs-number">10</span>}                                     <span class="hljs-comment"># '&lt;el&gt;      '</span>
{&lt;el&gt;:^<span class="hljs-number">10</span>}                                     <span class="hljs-comment"># '   &lt;el&gt;   '</span>
{&lt;el&gt;:&gt;<span class="hljs-number">10</span>}                                     <span class="hljs-comment"># '      &lt;el&gt;'</span>
{&lt;el&gt;:.&lt;<span class="hljs-number">10</span>}                                    <span class="hljs-comment"># '&lt;el&gt;......'</span>
{&lt;el&gt;:<span class="hljs-number">0</span>}                                       <span class="hljs-comment"># '&lt;el&gt;'</span>
</code></pre></div>

<div><h3 id="strings">Strings</h3><p><strong><code class="python hljs"><span class="hljs-string">'!r'</span></code> calls object's <a href="#class">repr()</a> method, instead of <a href="#class">str()</a>, to get a string.</strong></p><pre><code class="python language-python hljs">{<span class="hljs-string">'abcde'</span>!r:<span class="hljs-number">10</span>}                                 <span class="hljs-comment"># "'abcde'   "</span>
{<span class="hljs-string">'abcde'</span>:<span class="hljs-number">10.3</span>}                                 <span class="hljs-comment"># 'abc       '</span>
{<span class="hljs-string">'abcde'</span>:<span class="hljs-number">.3</span>}                                   <span class="hljs-comment"># 'abc'</span>
</code></pre></div>


<div><h3 id="numbers-1">Numbers</h3><pre><code class="python language-python hljs">{ <span class="hljs-number">123456</span>:<span class="hljs-number">10</span>,}                                  <span class="hljs-comment"># '   123,456'</span>
{ <span class="hljs-number">123456</span>:<span class="hljs-number">10</span>_}                                  <span class="hljs-comment"># '   123_456'</span>
{ <span class="hljs-number">123456</span>:+<span class="hljs-number">10</span>}                                  <span class="hljs-comment"># '   +123456'</span>
{<span class="hljs-number">-123456</span>:=<span class="hljs-number">10</span>}                                  <span class="hljs-comment"># '-   123456'</span>
{ <span class="hljs-number">123456</span>: }                                    <span class="hljs-comment"># ' 123456'</span>
{<span class="hljs-number">-123456</span>: }                                    <span class="hljs-comment"># '-123456'</span>
</code></pre></div>

<div><h3 id="floats">Floats</h3><pre><code class="python language-python hljs">{<span class="hljs-number">1.23456</span>:<span class="hljs-number">10.3</span>}                                 <span class="hljs-comment"># '      1.23'</span>
{<span class="hljs-number">1.23456</span>:<span class="hljs-number">10.3</span>f}                                <span class="hljs-comment"># '     1.235'</span>
{<span class="hljs-number">1.23456</span>:<span class="hljs-number">10.3</span>e}                                <span class="hljs-comment"># ' 1.235e+00'</span>
{<span class="hljs-number">1.23456</span>:<span class="hljs-number">10.3</span>%}                                <span class="hljs-comment"># '  123.456%'</span>
</code></pre></div>

<div><h4 id="comparisonofpresentationtypes">Comparison of presentation types:</h4><pre><code class="text language-text">┏━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━┓
┃               │    {&lt;float&gt;}    │   {&lt;float&gt;:f}   │   {&lt;float&gt;:e}   │   {&lt;float&gt;:%}   ┃
┠───────────────┼─────────────────┼─────────────────┼─────────────────┼─────────────────┨
┃   0.000056789 │    '5.6789e-05' │     '0.000057'  │  '5.678900e-05' │     '0.005679%' ┃
┃   0.00056789  │    '0.00056789' │     '0.000568'  │  '5.678900e-04' │     '0.056789%' ┃
┃   0.0056789   │    '0.0056789'  │     '0.005679'  │  '5.678900e-03' │     '0.567890%' ┃
┃   0.056789    │    '0.056789'   │     '0.056789'  │  '5.678900e-02' │     '5.678900%' ┃
┃   0.56789     │    '0.56789'    │     '0.567890'  │  '5.678900e-01' │    '56.789000%' ┃
┃   5.6789      │    '5.6789'     │     '5.678900'  │  '5.678900e+00' │   '567.890000%' ┃
┃  56.789       │   '56.789'      │    '56.789000'  │  '5.678900e+01' │  '5678.900000%' ┃
┃ 567.89        │  '567.89'       │   '567.890000'  │  '5.678900e+02' │ '56789.000000%' ┃
┗━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━┛
</code></pre></div>

<pre><code class="text language-text">┏━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━┓
┃               │   {&lt;float&gt;:.2}  │  {&lt;float&gt;:.2f}  │  {&lt;float&gt;:.2e}  │  {&lt;float&gt;:.2%}  ┃
┠───────────────┼─────────────────┼─────────────────┼─────────────────┼─────────────────┨
┃   0.000056789 │    '5.7e-05'    │       '0.00'    │    '5.68e-05'   │       '0.01%'   ┃
┃   0.00056789  │    '0.00057'    │       '0.00'    │    '5.68e-04'   │       '0.06%'   ┃
┃   0.0056789   │    '0.0057'     │       '0.01'    │    '5.68e-03'   │       '0.57%'   ┃
┃   0.056789    │    '0.057'      │       '0.06'    │    '5.68e-02'   │       '5.68%'   ┃
┃   0.56789     │    '0.57'       │       '0.57'    │    '5.68e-01'   │      '56.79%'   ┃
┃   5.6789      │    '5.7'        │       '5.68'    │    '5.68e+00'   │     '567.89%'   ┃
┃  56.789       │    '5.7e+01'    │      '56.79'    │    '5.68e+01'   │    '5678.90%'   ┃
┃ 567.89        │    '5.7e+02'    │     '567.89'    │    '5.68e+02'   │   '56789.00%'   ┃
┗━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━┛
</code></pre>
<div><h3 id="ints">Ints</h3><pre><code class="python language-python hljs">{<span class="hljs-number">90</span>:c}                                   <span class="hljs-comment"># 'Z'</span>
{<span class="hljs-number">90</span>:b}                                   <span class="hljs-comment"># '1011010'</span>
{<span class="hljs-number">90</span>:X}                                   <span class="hljs-comment"># '5A'</span>
</code></pre></div>

<div><h2 id="numbers"><a href="#numbers" name="numbers">#</a>Numbers</h2><div><h3 id="types">Types</h3><pre><code class="python language-python hljs">&lt;int&gt;      = int(&lt;float/str/bool&gt;)       <span class="hljs-comment"># Or: math.floor(&lt;float&gt;)</span>
&lt;float&gt;    = float(&lt;int/str/bool&gt;)       <span class="hljs-comment"># Or: &lt;real&gt;e±&lt;int&gt;</span>
&lt;complex&gt;  = complex(real=<span class="hljs-number">0</span>, imag=<span class="hljs-number">0</span>)     <span class="hljs-comment"># Or: &lt;real&gt; ± &lt;real&gt;j</span>
&lt;Fraction&gt; = fractions.Fraction(<span class="hljs-number">0</span>, <span class="hljs-number">1</span>)    <span class="hljs-comment"># Or: Fraction(numerator=0, denominator=1)</span>
&lt;Decimal&gt;  = decimal.Decimal(&lt;str/int&gt;)  <span class="hljs-comment"># Or: Decimal((sign, digits, exponent))</span>
</code></pre></div></div>


<ul>
<li><strong><code class="python hljs"><span class="hljs-string">'int(&lt;str&gt;)'</span></code> and <code class="python hljs"><span class="hljs-string">'float(&lt;str&gt;)'</span></code> raise ValueError on malformed strings.</strong></li>
<li><strong>Decimal numbers can be represented exactly, unlike floats where <code class="python hljs"><span class="hljs-string">'1.1 + 2.2 != 3.3'</span></code>.</strong></li>
<li><strong>Precision of decimal operations is set with: <code class="python hljs"><span class="hljs-string">'decimal.getcontext().prec = &lt;int&gt;'</span></code>.</strong></li>
</ul>
<div><h3 id="basicfunctions">Basic Functions</h3><pre><code class="python language-python hljs">&lt;num&gt; = pow(&lt;num&gt;, &lt;num&gt;)                <span class="hljs-comment"># Or: &lt;num&gt; ** &lt;num&gt;</span>
&lt;num&gt; = abs(&lt;num&gt;)                       <span class="hljs-comment"># &lt;float&gt; = abs(&lt;complex&gt;)</span>
&lt;num&gt; = round(&lt;num&gt; [, ±ndigits])        <span class="hljs-comment"># `round(126, -1) == 130`</span>
</code></pre></div>

<div><h3 id="math">Math</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> e, pi, inf, nan, isinf, isnan
<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> cos, acos, sin, asin, tan, atan, degrees, radians
<span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> log, log10, log2
</code></pre></div>

<div><h3 id="statistics">Statistics</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> statistics <span class="hljs-keyword">import</span> mean, median, variance, stdev, pvariance, pstdev
</code></pre></div>

<div><h3 id="random">Random</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> random <span class="hljs-keyword">import</span> random, randint, choice, shuffle
&lt;float&gt; = random()
&lt;int&gt;   = randint(from_inclusive, to_inclusive)
&lt;el&gt;    = choice(&lt;list&gt;)
shuffle(&lt;list&gt;)
</code></pre></div>

<div><h3 id="binhex">Bin, Hex</h3><pre><code class="python language-python hljs">&lt;int&gt; = ±<span class="hljs-number">0</span>b&lt;bin&gt;                         <span class="hljs-comment"># Or: ±0x&lt;hex&gt;</span>
&lt;int&gt; = int(<span class="hljs-string">'±&lt;bin&gt;'</span>, <span class="hljs-number">2</span>)                 <span class="hljs-comment"># Or: int('±&lt;hex&gt;', 16)</span>
&lt;int&gt; = int(<span class="hljs-string">'±0b&lt;bin&gt;'</span>, <span class="hljs-number">0</span>)               <span class="hljs-comment"># Or: int('±0x&lt;hex&gt;', 0)</span>
&lt;str&gt; = bin(&lt;int&gt;)                       <span class="hljs-comment"># Returns '[-]0b&lt;bin&gt;'.</span>
</code></pre></div>

<div><h3 id="bitwiseoperators">Bitwise Operators</h3><pre><code class="python language-python hljs">&lt;int&gt; = &lt;int&gt; &amp; &lt;int&gt;                    <span class="hljs-comment"># And</span>
&lt;int&gt; = &lt;int&gt; | &lt;int&gt;                    <span class="hljs-comment"># Or</span>
&lt;int&gt; = &lt;int&gt; ^ &lt;int&gt;                    <span class="hljs-comment"># Xor (0 if both bits equal)</span>
&lt;int&gt; = &lt;int&gt; &lt;&lt; n_bits                  <span class="hljs-comment"># Shift left (&gt;&gt; for right)</span>
&lt;int&gt; = ~&lt;int&gt;                           <span class="hljs-comment"># Not (also: -&lt;int&gt; - 1)</span>
</code></pre></div>

<div><h2 id="combinatorics"><a href="#combinatorics" name="combinatorics">#</a>Combinatorics</h2><ul>
<li><strong>Every function returns an iterator.</strong></li>
<li><strong>If you want to print the iterator, you need to pass it to the list() function first!</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> itertools <span class="hljs-keyword">import</span> product, combinations, combinations_with_replacement, permutations
</code></pre></div>


<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>product([<span class="hljs-number">0</span>, <span class="hljs-number">1</span>], repeat=<span class="hljs-number">3</span>)
[(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>), (<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">1</span>), (<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">0</span>), (<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>), ..., (<span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>)]
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>product(<span class="hljs-string">'abc'</span>, <span class="hljs-string">'abc'</span>)                    <span class="hljs-comment">#   a  b  c</span>
[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),         <span class="hljs-comment"># a x  x  x</span>
 (<span class="hljs-string">'b'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>),         <span class="hljs-comment"># b x  x  x</span>
 (<span class="hljs-string">'c'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'c'</span>)]         <span class="hljs-comment"># c x  x  x</span>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>combinations(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>)                   <span class="hljs-comment">#   a  b  c</span>
[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),                     <span class="hljs-comment"># a .  x  x</span>
 (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>)]                                 <span class="hljs-comment"># b .  .  x</span>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>combinations_with_replacement(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>)  <span class="hljs-comment">#   a  b  c</span>
[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),         <span class="hljs-comment"># a x  x  x</span>
 (<span class="hljs-string">'b'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>),                     <span class="hljs-comment"># b .  x  x</span>
 (<span class="hljs-string">'c'</span>, <span class="hljs-string">'c'</span>)]                                 <span class="hljs-comment"># c .  .  x</span>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>permutations(<span class="hljs-string">'abc'</span>, <span class="hljs-number">2</span>)                   <span class="hljs-comment">#   a  b  c</span>
[(<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>), (<span class="hljs-string">'a'</span>, <span class="hljs-string">'c'</span>),                     <span class="hljs-comment"># a .  x  x</span>
 (<span class="hljs-string">'b'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>),                     <span class="hljs-comment"># b x  .  x</span>
 (<span class="hljs-string">'c'</span>, <span class="hljs-string">'a'</span>), (<span class="hljs-string">'c'</span>, <span class="hljs-string">'b'</span>)]                     <span class="hljs-comment"># c x  x  .</span>
</code></pre>
<div><h2 id="datetime"><a href="#datetime" name="datetime">#</a>Datetime</h2><ul>
<li><strong>Module 'datetime' provides 'date' <code class="apache hljs"><span class="hljs-section">&lt;D&gt;</span></code>, 'time' <code class="apache hljs"><span class="hljs-section">&lt;T&gt;</span></code>, 'datetime' <code class="apache hljs"><span class="hljs-section">&lt;DT&gt;</span></code> and 'timedelta' <code class="apache hljs"><span class="hljs-section">&lt;TD&gt;</span></code> classes. All are immutable and hashable.</strong></li>
<li><strong>Time and datetime objects can be 'aware' <code class="apache hljs"><span class="hljs-section">&lt;a&gt;</span></code>, meaning they have defined timezone, or 'naive' <code class="apache hljs"><span class="hljs-section">&lt;n&gt;</span></code>, meaning they don't.</strong></li>
<li><strong>If object is naive, it is presumed to be in the system's timezone.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> datetime <span class="hljs-keyword">import</span> date, time, datetime, timedelta
<span class="hljs-keyword">from</span> dateutil.tz <span class="hljs-keyword">import</span> UTC, tzlocal, gettz, resolve_imaginary
</code></pre></div>


<div><h3 id="constructors">Constructors</h3><pre><code class="python language-python apache hljs">&lt;D&gt;  = date(year, month, day)
&lt;T&gt;  = time(hour=<span class="hljs-number">0</span>, minute=<span class="hljs-number">0</span>, second=<span class="hljs-number">0</span>, microsecond=<span class="hljs-number">0</span>, tzinfo=<span class="hljs-keyword">None</span>, fold=<span class="hljs-number">0</span>)
&lt;DT&gt; = datetime(year, month, day, hour=<span class="hljs-number">0</span>, minute=<span class="hljs-number">0</span>, second=<span class="hljs-number">0</span>, ...)
&lt;TD&gt; = timedelta(days=<span class="hljs-number">0</span>, seconds=<span class="hljs-number">0</span>, microseconds=<span class="hljs-number">0</span>, milliseconds=<span class="hljs-number">0</span>,
                 minutes=<span class="hljs-number">0</span>, hours=<span class="hljs-number">0</span>, weeks=<span class="hljs-number">0</span>)
</code></pre></div>

<ul>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'&lt;D/DT&gt;.weekday()'</span></code> to get the day of the week (Mon == 0).</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'fold=1'</span></code> means the second pass in case of time jumping back for one hour.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'&lt;DTa&gt; = resolve_imaginary(&lt;DTa&gt;)'</span></code> fixes DTs that fall into the missing hour.</strong></li>
</ul>
<div><h3 id="now">Now</h3><pre><code class="python language-python hljs">&lt;D/DTn&gt;  = D/DT.today()                     <span class="hljs-comment"># Current local date or naive datetime.</span>
&lt;DTn&gt;    = DT.utcnow()                      <span class="hljs-comment"># Naive datetime from current UTC time.</span>
&lt;DTa&gt;    = DT.now(&lt;tzinfo&gt;)                 <span class="hljs-comment"># Aware datetime from current tz time.</span>
</code></pre></div>

<ul>
<li><strong>To extract time use <code class="python hljs"><span class="hljs-string">'&lt;DTn&gt;.time()'</span></code>, <code class="python hljs"><span class="hljs-string">'&lt;DTa&gt;.time()'</span></code> or <code class="python hljs"><span class="hljs-string">'&lt;DTa&gt;.timetz()'</span></code>.</strong></li>
</ul>
<div><h3 id="timezone">Timezone</h3><pre><code class="python language-python apache hljs">&lt;tzinfo&gt; = UTC                              <span class="hljs-comment"># UTC timezone. London without DST.</span>
&lt;tzinfo&gt; = tzlocal()                        <span class="hljs-comment"># Local timezone. Also gettz().</span>
&lt;tzinfo&gt; = gettz(<span class="hljs-string">'&lt;Continent&gt;/&lt;City&gt;'</span>)      <span class="hljs-comment"># 'Continent/City_Name' timezone or None.</span>
&lt;DTa&gt;    = &lt;DT&gt;.astimezone(&lt;tzinfo&gt;)        <span class="hljs-comment"># Datetime, converted to passed timezone.</span>
&lt;Ta/DTa&gt; = &lt;T/DT&gt;.replace(tzinfo=&lt;tzinfo&gt;)  <span class="hljs-comment"># Unconverted object with new timezone.</span>
</code></pre></div>

<div><h3 id="encode">Encode</h3><pre><code class="python language-python apache hljs">&lt;D/T/DT&gt; = D/T/DT.fromisoformat(<span class="hljs-string">'&lt;iso&gt;'</span>)    <span class="hljs-comment"># Object from ISO string. Raises ValueError.</span>
&lt;DT&gt;     = DT.strptime(&lt;str&gt;, <span class="hljs-string">'&lt;format&gt;'</span>)   <span class="hljs-comment"># Datetime from str, according to format.</span>
&lt;D/DTn&gt;  = D/DT.fromordinal(&lt;int&gt;)          <span class="hljs-comment"># D/DTn from days since Christ, at midnight.</span>
&lt;DTn&gt;    = DT.fromtimestamp(&lt;real&gt;)         <span class="hljs-comment"># Local time DTn from seconds since Epoch.</span>
&lt;DTa&gt;    = DT.fromtimestamp(&lt;real&gt;, &lt;tz.&gt;)  <span class="hljs-comment"># Aware datetime from seconds since Epoch.</span>
</code></pre></div>

<ul>
<li><strong>ISO strings come in following forms: <code class="python hljs"><span class="hljs-string">'YYYY-MM-DD'</span></code>, <code class="python hljs"><span class="hljs-string">'HH:MM:SS.ffffff[±&lt;offset&gt;]'</span></code>, or both separated by an arbitrary character. Offset is formatted as: <code class="python hljs"><span class="hljs-string">'HH:MM'</span></code>.</strong></li>
<li><strong>Epoch on Unix systems is: <code class="python hljs"><span class="hljs-string">'1970-01-01 00:00 UTC'</span></code>, <code class="python hljs"><span class="hljs-string">'1970-01-01 01:00 CET'</span></code>, …</strong></li>
</ul>
<div><h3 id="decode">Decode</h3><pre><code class="python language-python hljs">&lt;str&gt;    = &lt;D/T/DT&gt;.isoformat(sep=<span class="hljs-string">'T'</span>)      <span class="hljs-comment"># Also timespec='auto/hours/minutes/seconds'.</span>
&lt;str&gt;    = &lt;D/T/DT&gt;.strftime(<span class="hljs-string">'&lt;format&gt;'</span>)    <span class="hljs-comment"># Custom string representation.</span>
&lt;int&gt;    = &lt;D/DT&gt;.toordinal()               <span class="hljs-comment"># Days since Christ, ignoring time and tz.</span>
&lt;float&gt;  = &lt;DTn&gt;.timestamp()                <span class="hljs-comment"># Seconds since Epoch, from DTn in local tz.</span>
&lt;float&gt;  = &lt;DTa&gt;.timestamp()                <span class="hljs-comment"># Seconds since Epoch, from DTa.</span>
</code></pre></div>

<div><h3 id="format-1">Format</h3><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> datetime <span class="hljs-keyword">import</span> datetime
<span class="hljs-meta">&gt;&gt;&gt; </span>dt = datetime.strptime(<span class="hljs-string">'2015-05-14 23:39:00.00 +0200'</span>, <span class="hljs-string">'%Y-%m-%d %H:%M:%S.%f %z'</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>dt.strftime(<span class="hljs-string">"%A, %dth of %B '%y, %I:%M%p %Z"</span>)
<span class="hljs-string">"Thursday, 14th of May '15, 11:39PM UTC+02:00"</span>
</code></pre></div>

<ul>
<li><strong>When parsing, <code class="python hljs"><span class="hljs-string">'%z'</span></code> also accepts <code class="python hljs"><span class="hljs-string">'±HH:MM'</span></code>.</strong></li>
<li><strong>For abbreviated weekday and month use <code class="python hljs"><span class="hljs-string">'%a'</span></code> and <code class="python hljs"><span class="hljs-string">'%b'</span></code>.</strong></li>
</ul>
<div><h3 id="arithmetics">Arithmetics</h3><pre><code class="python language-python apache hljs">&lt;D/DT&gt;   = &lt;D/DT&gt;   ± &lt;TD&gt;                  <span class="hljs-comment"># Returned datetime can fall into missing hour.</span>
&lt;TD&gt;     = &lt;D/DTn&gt;  - &lt;D/DTn&gt;               <span class="hljs-comment"># Returns the difference, ignoring time jumps.</span>
&lt;TD&gt;     = &lt;DTa&gt;    - &lt;DTa&gt;                 <span class="hljs-comment"># Ignores time jumps if they share tzinfo object.</span>
&lt;TD&gt;     = &lt;DT_UTC&gt; - &lt;DT_UTC&gt;              <span class="hljs-comment"># Convert DTs to UTC to get the actual delta.</span>
</code></pre></div>

<div><h2 id="arguments"><a href="#arguments" name="arguments">#</a>Arguments</h2><div><h3 id="insidefunctioncall">Inside Function Call</h3><pre><code class="python language-python hljs">&lt;function&gt;(&lt;positional_args&gt;)                  <span class="hljs-comment"># f(0, 0)</span>
&lt;function&gt;(&lt;keyword_args&gt;)                     <span class="hljs-comment"># f(x=0, y=0)</span>
&lt;function&gt;(&lt;positional_args&gt;, &lt;keyword_args&gt;)  <span class="hljs-comment"># f(0, y=0)</span>
</code></pre></div></div>


<div><h3 id="insidefunctiondefinition">Inside Function Definition</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(&lt;nondefault_args&gt;)</span>:</span>                      <span class="hljs-comment"># def f(x, y):</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(&lt;default_args&gt;)</span>:</span>                         <span class="hljs-comment"># def f(x=0, y=0):</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(&lt;nondefault_args&gt;, &lt;default_args&gt;)</span>:</span>      <span class="hljs-comment"># def f(x, y=0):</span>
</code></pre></div>

<div><h2 id="splatoperator"><a href="#splatoperator" name="splatoperator">#</a>Splat Operator</h2><div><h3 id="insidefunctioncall-1">Inside Function Call</h3><p><strong>Splat expands a collection into positional arguments, while splatty-splat expands a dictionary into keyword arguments.</strong></p><pre><code class="python language-python hljs">args   = (<span class="hljs-number">1</span>, <span class="hljs-number">2</span>)
kwargs = {<span class="hljs-string">'x'</span>: <span class="hljs-number">3</span>, <span class="hljs-string">'y'</span>: <span class="hljs-number">4</span>, <span class="hljs-string">'z'</span>: <span class="hljs-number">5</span>}
func(*args, **kwargs)
</code></pre></div></div>



<div><h4 id="isthesameas">Is the same as:</h4><pre><code class="python language-python hljs">func(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, x=<span class="hljs-number">3</span>, y=<span class="hljs-number">4</span>, z=<span class="hljs-number">5</span>)
</code></pre></div>

<div><h3 id="insidefunctiondefinition-1">Inside Function Definition</h3><p><strong>Splat combines zero or more positional arguments into a tuple, while splatty-splat combines zero or more keyword arguments into a dictionary.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(*a)</span>:</span>
    <span class="hljs-keyword">return</span> sum(a)
</code></pre></div>


<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>add(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
<span class="hljs-number">6</span>
</code></pre>
<div><h4 id="legalargumentcombinations">Legal argument combinations:</h4><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, y, z)</span>:</span>                <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*, x, y, z)</span>:</span>             <span class="hljs-comment"># f(x=1, y=2, z=3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *, y, z)</span>:</span>             <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, y, *, z)</span>:</span>             <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3)</span>
</code></pre></div>

<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args)</span>:</span>                  <span class="hljs-comment"># f(1, 2, 3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *args)</span>:</span>               <span class="hljs-comment"># f(1, 2, 3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args, z)</span>:</span>               <span class="hljs-comment"># f(1, 2, z=3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *args, z)</span>:</span>            <span class="hljs-comment"># f(1, 2, z=3)</span>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(**kwargs)</span>:</span>               <span class="hljs-comment"># f(x=1, y=2, z=3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, **kwargs)</span>:</span>            <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*, x, **kwargs)</span>:</span>         <span class="hljs-comment"># f(x=1, y=2, z=3)</span>
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args, **kwargs)</span>:</span>        <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *args, **kwargs)</span>:</span>     <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3) | f(1, 2, 3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(*args, y, **kwargs)</span>:</span>     <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">f</span><span class="hljs-params">(x, *args, z, **kwargs)</span>:</span>  <span class="hljs-comment"># f(x=1, y=2, z=3) | f(1, y=2, z=3) | f(1, 2, z=3)</span>
</code></pre>
<div><h3 id="otheruses">Other Uses</h3><pre><code class="python language-python hljs">&lt;list&gt;  = [*&lt;collection&gt; [, ...]]
&lt;set&gt;   = {*&lt;collection&gt; [, ...]}
&lt;tuple&gt; = (*&lt;collection&gt;, [...])
&lt;dict&gt;  = {**&lt;dict&gt; [, ...]}
</code></pre></div>

<pre><code class="python language-python hljs">head, *body, tail = &lt;collection&gt;
</code></pre>
<div><h2 id="inline"><a href="#inline" name="inline">#</a>Inline</h2><div><h3 id="lambda">Lambda</h3><pre><code class="python language-python hljs">&lt;function&gt; = <span class="hljs-keyword">lambda</span>: &lt;return_value&gt;
&lt;function&gt; = <span class="hljs-keyword">lambda</span> &lt;argument_1&gt;, &lt;argument_2&gt;: &lt;return_value&gt;
</code></pre></div></div>


<div><h3 id="comprehensions">Comprehensions</h3><pre><code class="python language-python hljs">&lt;list&gt; = [i+<span class="hljs-number">1</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)]                   <span class="hljs-comment"># [1, 2, ..., 10]</span>
&lt;set&gt;  = {i <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>) <span class="hljs-keyword">if</span> i &gt; <span class="hljs-number">5</span>}            <span class="hljs-comment"># {6, 7, 8, 9}</span>
&lt;iter&gt; = (i+<span class="hljs-number">5</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>))                   <span class="hljs-comment"># (5, 6, ..., 14)</span>
&lt;dict&gt; = {i: i*<span class="hljs-number">2</span> <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)}                <span class="hljs-comment"># {0: 0, 1: 2, ..., 9: 18}</span>
</code></pre></div>

<pre><code class="python language-python hljs">out = [i+j <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>) <span class="hljs-keyword">for</span> j <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)]
</code></pre>
<div><h4 id="isthesameas-1">Is the same as:</h4><pre><code class="python language-python hljs">out = []
<span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>):
    <span class="hljs-keyword">for</span> j <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>):
        out.append(i+j)
</code></pre></div>

<div><h3 id="mapfilterreduce">Map, Filter, Reduce</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> reduce
&lt;iter&gt; = map(<span class="hljs-keyword">lambda</span> x: x + <span class="hljs-number">1</span>, range(<span class="hljs-number">10</span>))            <span class="hljs-comment"># (1, 2, ..., 10)</span>
&lt;iter&gt; = filter(<span class="hljs-keyword">lambda</span> x: x &gt; <span class="hljs-number">5</span>, range(<span class="hljs-number">10</span>))         <span class="hljs-comment"># (6, 7, 8, 9)</span>
&lt;obj&gt;  = reduce(<span class="hljs-keyword">lambda</span> out, x: out + x, range(<span class="hljs-number">10</span>))  <span class="hljs-comment"># 45</span>
</code></pre></div>

<div><h3 id="anyall">Any, All</h3><pre><code class="python language-python hljs">&lt;bool&gt; = any(&lt;collection&gt;)                          <span class="hljs-comment"># False if empty.</span>
&lt;bool&gt; = all(el[<span class="hljs-number">1</span>] <span class="hljs-keyword">for</span> el <span class="hljs-keyword">in</span> &lt;collection&gt;)          <span class="hljs-comment"># True if empty.</span>
</code></pre></div>

<div><h3 id="ifelse">If - Else</h3><pre><code class="python language-python hljs">&lt;obj&gt; = &lt;expression_if_true&gt; <span class="hljs-keyword">if</span> &lt;condition&gt; <span class="hljs-keyword">else</span> &lt;expression_if_false&gt;
</code></pre></div>

<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>[a <span class="hljs-keyword">if</span> a <span class="hljs-keyword">else</span> <span class="hljs-string">'zero'</span> <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> (<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)]
[<span class="hljs-string">'zero'</span>, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]
</code></pre>
<div><h3 id="namedtupleenumdataclass">Namedtuple, Enum, Dataclass</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> namedtuple
Point     = namedtuple(<span class="hljs-string">'Point'</span>, <span class="hljs-string">'x y'</span>)
point     = Point(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>)
</code></pre></div>

<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> enum <span class="hljs-keyword">import</span> Enum
Direction = Enum(<span class="hljs-string">'Direction'</span>, <span class="hljs-string">'n e s w'</span>)
direction = Direction.n
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> dataclasses <span class="hljs-keyword">import</span> make_dataclass
Creature  = make_dataclass(<span class="hljs-string">'Creature'</span>, [<span class="hljs-string">'location'</span>, <span class="hljs-string">'direction'</span>])
creature  = Creature(Point(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>), Direction.n)
</code></pre>
<div><h2 id="closure"><a href="#closure" name="closure">#</a>Closure</h2><p><strong>We have a closure in Python when:</strong></p><ul>
<li><strong>A nested function references a value of its enclosing function and then</strong></li>
<li><strong>the enclosing function returns the nested function.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_multiplier</span><span class="hljs-params">(a)</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(b)</span>:</span>
        <span class="hljs-keyword">return</span> a * b
    <span class="hljs-keyword">return</span> out
</code></pre></div>



<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>multiply_by_3 = get_multiplier(<span class="hljs-number">3</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>multiply_by_3(<span class="hljs-number">10</span>)
<span class="hljs-number">30</span>
</code></pre>
<ul>
<li><strong>If multiple nested functions within enclosing function reference the same value, that value gets shared.</strong></li>
<li><strong>To dynamically access function's first free variable use <code class="python hljs"><span class="hljs-string">'&lt;function&gt;.__closure__[0].cell_contents'</span></code>.</strong></li>
</ul>
<div><h3 id="partial">Partial</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> partial
&lt;function&gt; = partial(&lt;function&gt; [, &lt;arg_1&gt;, &lt;arg_2&gt;, ...])
</code></pre></div>

<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">import</span> operator <span class="hljs-keyword">as</span> op
<span class="hljs-meta">&gt;&gt;&gt; </span>multiply_by_3 = partial(op.mul, <span class="hljs-number">3</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>multiply_by_3(<span class="hljs-number">10</span>)
<span class="hljs-number">30</span>
</code></pre>
<ul>
<li><strong>Partial is also useful in cases when function needs to be passed as an argument, because it enables us to set its arguments beforehand.</strong></li>
<li><strong>A few examples being: <code class="python hljs"><span class="hljs-string">'defaultdict(&lt;function&gt;)'</span></code>, <code class="python hljs"><span class="hljs-string">'iter(&lt;function&gt;, to_exclusive)'</span></code> and dataclass's <code class="python hljs"><span class="hljs-string">'field(default_factory=&lt;function&gt;)'</span></code>.</strong></li>
</ul>
<div><h3 id="nonlocal">Non-Local</h3><p><strong>If variable is being assigned to anywhere in the scope, it is regarded as a local variable, unless it is declared as a 'global' or a 'nonlocal'.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_counter</span><span class="hljs-params">()</span>:</span>
    i = <span class="hljs-number">0</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">()</span>:</span>
        <span class="hljs-keyword">nonlocal</span> i
        i += <span class="hljs-number">1</span>
        <span class="hljs-keyword">return</span> i
    <span class="hljs-keyword">return</span> out
</code></pre></div>


<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>counter = get_counter()
<span class="hljs-meta">&gt;&gt;&gt; </span>counter(), counter(), counter()
(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
</code></pre>
<div><h2 id="decorator"><a href="#decorator" name="decorator">#</a>Decorator</h2><p><strong>A decorator takes a function, adds some functionality and returns it.</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">@decorator_name</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">function_that_gets_passed_to_decorator</span><span class="hljs-params">()</span>:</span>
    ...
</code></pre></div>


<div><h3 id="debuggerexample">Debugger Example</h3><p><strong>Decorator that prints function's name every time it gets called.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> wraps

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">debug</span><span class="hljs-params">(func)</span>:</span>
<span class="hljs-meta">    @wraps(func)</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(*args, **kwargs)</span>:</span>
        print(func.__name__)
        <span class="hljs-keyword">return</span> func(*args, **kwargs)
    <span class="hljs-keyword">return</span> out

<span class="hljs-meta">@debug</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(x, y)</span>:</span>
    <span class="hljs-keyword">return</span> x + y
</code></pre></div>


<ul>
<li><strong>Wraps is a helper decorator that copies the metadata of the passed function (func) to the function it is wrapping (out).</strong></li>
<li><strong>Without it <code class="python hljs"><span class="hljs-string">'add.__name__'</span></code> would return <code class="python hljs"><span class="hljs-string">'out'</span></code>.</strong></li>
</ul>
<div><h3 id="lrucache">LRU Cache</h3><p><strong>Decorator that caches function's return values. All function's arguments must be hashable.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> lru_cache

<span class="hljs-meta">@lru_cache(maxsize=None)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">fib</span><span class="hljs-params">(n)</span>:</span>
    <span class="hljs-keyword">return</span> n <span class="hljs-keyword">if</span> n &lt; <span class="hljs-number">2</span> <span class="hljs-keyword">else</span> fib(n-<span class="hljs-number">2</span>) + fib(n-<span class="hljs-number">1</span>)
</code></pre></div>


<ul>
<li><strong>CPython interpreter limits recursion depth to 1000 by default. To increase it use <code class="python hljs"><span class="hljs-string">'sys.setrecursionlimit(&lt;depth&gt;)'</span></code>.</strong></li>
</ul>
<div><h3 id="parametrizeddecorator">Parametrized Decorator</h3><p><strong>A decorator that accepts arguments and returns a normal decorator that accepts a function.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> wraps

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">debug</span><span class="hljs-params">(print_result=False)</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">decorator</span><span class="hljs-params">(func)</span>:</span>
<span class="hljs-meta">        @wraps(func)</span>
        <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">out</span><span class="hljs-params">(*args, **kwargs)</span>:</span>
            result = func(*args, **kwargs)
            print(func.__name__, result <span class="hljs-keyword">if</span> print_result <span class="hljs-keyword">else</span> <span class="hljs-string">''</span>)
            <span class="hljs-keyword">return</span> result
        <span class="hljs-keyword">return</span> out
    <span class="hljs-keyword">return</span> decorator

<span class="hljs-meta">@debug(print_result=True)</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">add</span><span class="hljs-params">(x, y)</span>:</span>
    <span class="hljs-keyword">return</span> x + y
</code></pre></div>


<div><h2 id="class"><a href="#class" name="class">#</a>Class</h2><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">name</span>&gt;:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
        self.a = a
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__repr__</span><span class="hljs-params">(self)</span>:</span>
        class_name = self.__class__.__name__
        <span class="hljs-keyword">return</span> <span class="hljs-string">f'<span class="hljs-subst">{class_name}</span>(<span class="hljs-subst">{self.a!r}</span>)'</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__str__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> str(self.a)

<span class="hljs-meta">    @classmethod</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_class_name</span><span class="hljs-params">(cls)</span>:</span>
        <span class="hljs-keyword">return</span> cls.__name__
</code></pre></div>

<ul>
<li><strong>Return value of repr() should be unambiguous and of str() readable.</strong></li>
<li><strong>If only repr() is defined, it will also be used for str().</strong></li>
</ul>
<div><h4 id="strusecases">Str() use cases:</h4><pre><code class="python language-python hljs">print(&lt;el&gt;)
print(<span class="hljs-string">f'<span class="hljs-subst">{&lt;el&gt;}</span>'</span>)
<span class="hljs-keyword">raise</span> Exception(&lt;el&gt;)
loguru.logger.debug(&lt;el&gt;)
csv.writer(&lt;file&gt;).writerow([&lt;el&gt;])
</code></pre></div>

<div><h4 id="reprusecases">Repr() use cases:</h4><pre><code class="python language-python hljs">print([&lt;el&gt;])
print(<span class="hljs-string">f'<span class="hljs-subst">{&lt;el&gt;!r}</span>'</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>&lt;el&gt;
loguru.logger.exception()
Z = dataclasses.make_dataclass(<span class="hljs-string">'Z'</span>, [<span class="hljs-string">'a'</span>]); print(Z(&lt;el&gt;))
</code></pre></div>

<div><h3 id="constructoroverloading">Constructor Overloading</h3><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">name</span>&gt;:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a=<span class="hljs-keyword">None</span>)</span>:</span>
        self.a = a
</code></pre></div>

<div><h3 id="inheritance">Inheritance</h3><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Person</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name, age)</span>:</span>
        self.name = name
        self.age  = age

<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Employee</span><span class="hljs-params">(Person)</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, name, age, staff_num)</span>:</span>
        super().__init__(name, age)
        self.staff_num = staff_num
</code></pre></div>

<div><h3 id="multipleinheritance">Multiple Inheritance</h3><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">A</span>:</span> <span class="hljs-keyword">pass</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">B</span>:</span> <span class="hljs-keyword">pass</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">C</span><span class="hljs-params">(A, B)</span>:</span> <span class="hljs-keyword">pass</span>
</code></pre></div>

<p><strong>MRO determines the order in which parent classes are traversed when searching for a method:</strong></p>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>C.mro()
[&lt;<span class="hljs-class"><span class="hljs-title">class</span> '<span class="hljs-title">C</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">A</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">B</span>'&gt;, &lt;<span class="hljs-title">class</span> '<span class="hljs-title">object</span>'&gt;]
</span></code></pre>
<div><h3 id="property">Property</h3><p><strong>Pythonic way of implementing getters and setters.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyClass</span>:</span>
<span class="hljs-meta">    @property</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">a</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> self._a

<span class="hljs-meta">    @a.setter</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">a</span><span class="hljs-params">(self, value)</span>:</span>
        self._a = value
</code></pre></div>


<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>el = MyClass()
<span class="hljs-meta">&gt;&gt;&gt; </span>el.a = <span class="hljs-number">123</span>
<span class="hljs-meta">&gt;&gt;&gt; </span>el.a
<span class="hljs-number">123</span>
</code></pre>
<div><h3 id="dataclass">Dataclass</h3><p><strong>Decorator that automatically generates init(), repr() and eq() special methods.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> dataclasses <span class="hljs-keyword">import</span> dataclass, field

<span class="hljs-meta">@dataclass(order=False, frozen=False)</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">class_name</span>&gt;:</span>
    &lt;attr_name_1&gt;: &lt;type&gt;
    &lt;attr_name_2&gt;: &lt;type&gt; = &lt;default_value&gt;
    &lt;attr_name_3&gt;: list/dict/set = field(default_factory=list/dict/set)
</code></pre></div>


<ul>
<li><strong>Objects can be made sortable with <code class="python hljs"><span class="hljs-string">'order=True'</span></code> and immutable with <code class="python hljs"><span class="hljs-string">'frozen=True'</span></code>.</strong></li>
<li><strong>For object to be hashable, all attributes must be hashable and frozen must be True.</strong></li>
<li><strong>Function field() is needed because <code class="python hljs"><span class="hljs-string">'&lt;attr_name&gt;: list = []'</span></code> would make a list that is shared among all instances.</strong></li>
<li><strong>Default_factory can be any <a href="#callable">callable</a>.</strong></li>
</ul>
<div><h4 id="inline-1">Inline:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> dataclasses <span class="hljs-keyword">import</span> make_dataclass
&lt;class&gt; = make_dataclass(<span class="hljs-string">'&lt;class_name&gt;'</span>, &lt;coll_of_attribute_names&gt;)
&lt;class&gt; = make_dataclass(<span class="hljs-string">'&lt;class_name&gt;'</span>, &lt;coll_of_tuples&gt;)
&lt;tuple&gt; = (<span class="hljs-string">'&lt;attr_name&gt;'</span>, &lt;type&gt; [, &lt;default_value&gt;])</code></pre></div>

<div><h3 id="slots">Slots</h3><p><strong>Mechanism that restricts objects to attributes listed in 'slots' and significantly reduces their memory footprint.</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyClassWithSlots</span>:</span>
    __slots__ = [<span class="hljs-string">'a'</span>]
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self)</span>:</span>
        self.a = <span class="hljs-number">1</span>
</code></pre></div>


<div><h3 id="copy">Copy</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> copy <span class="hljs-keyword">import</span> copy, deepcopy
&lt;object&gt; = copy(&lt;object&gt;)
&lt;object&gt; = deepcopy(&lt;object&gt;)
</code></pre></div>

<div><h2 id="ducktypes"><a href="#ducktypes" name="ducktypes">#</a>Duck Types</h2><p><strong>A duck type is an implicit type that prescribes a set of special methods. Any object that has those methods defined is considered a member of that duck type.</strong></p><div><h3 id="comparable">Comparable</h3><ul>
<li><strong>If eq() method is not overridden, it returns <code class="python hljs"><span class="hljs-string">'id(self) == id(other)'</span></code>, which is the same as <code class="python hljs"><span class="hljs-string">'self is other'</span></code>.</strong></li>
<li><strong>That means all objects compare not equal by default.</strong></li>
<li><strong>Only the left side object has eq() method called, unless it returns NotImplemented, in which case the right object is consulted.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyComparable</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
        self.a = a
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__eq__</span><span class="hljs-params">(self, other)</span>:</span>
        <span class="hljs-keyword">if</span> isinstance(other, type(self)):
            <span class="hljs-keyword">return</span> self.a == other.a
        <span class="hljs-keyword">return</span> <span class="hljs-built_in">NotImplemented</span>
</code></pre></div></div>




<div><h3 id="hashable">Hashable</h3><ul>
<li><strong>Hashable object needs both hash() and eq() methods and its hash value should never change.</strong></li>
<li><strong>Hashable objects that compare equal must have the same hash value, meaning default hash() that returns <code class="python hljs"><span class="hljs-string">'id(self)'</span></code> will not do.</strong></li>
<li><strong>That is why Python automatically makes classes unhashable if you only implement eq().</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyHashable</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
        self._a = a
<span class="hljs-meta">    @property</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">a</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> self._a
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__eq__</span><span class="hljs-params">(self, other)</span>:</span>
        <span class="hljs-keyword">if</span> isinstance(other, type(self)):
            <span class="hljs-keyword">return</span> self.a == other.a
        <span class="hljs-keyword">return</span> <span class="hljs-built_in">NotImplemented</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__hash__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> hash(self.a)
</code></pre></div>


<div><h3 id="sortable">Sortable</h3><ul>
<li><strong>With total_ordering decorator, you only need to provide eq() and one of lt(), gt(), le() or ge() special methods.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> total_ordering

<span class="hljs-meta">@total_ordering</span>
<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MySortable</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
        self.a = a
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__eq__</span><span class="hljs-params">(self, other)</span>:</span>
        <span class="hljs-keyword">if</span> isinstance(other, type(self)):
            <span class="hljs-keyword">return</span> self.a == other.a
        <span class="hljs-keyword">return</span> <span class="hljs-built_in">NotImplemented</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__lt__</span><span class="hljs-params">(self, other)</span>:</span>
        <span class="hljs-keyword">if</span> isinstance(other, type(self)):
            <span class="hljs-keyword">return</span> self.a &lt; other.a
        <span class="hljs-keyword">return</span> <span class="hljs-built_in">NotImplemented</span>
</code></pre></div>


<div><h3 id="iterator-1">Iterator</h3><ul>
<li><strong>Any object that has methods next() and iter() is an iterator.</strong></li>
<li><strong>Next() should return next item or raise StopIteration.</strong></li>
<li><strong>Iter() should return 'self'.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Counter</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self)</span>:</span>
        self.i = <span class="hljs-number">0</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__next__</span><span class="hljs-params">(self)</span>:</span>
        self.i += <span class="hljs-number">1</span>
        <span class="hljs-keyword">return</span> self.i
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__iter__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> self
</code></pre></div>


<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>counter = Counter()
<span class="hljs-meta">&gt;&gt;&gt; </span>next(counter), next(counter), next(counter)
(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
</code></pre>
<div><h4 id="pythonhasmanydifferentiteratorobjects">Python has many different iterator objects:</h4><ul>
<li><strong>Iterators returned by the <a href="#iterator">iter()</a> function, such as list_iterator and set_iterator.</strong></li>
<li><strong>Objects returned by the <a href="#itertools">itertools</a> module, such as count, repeat and cycle.</strong></li>
<li><strong>Generators returned by the <a href="#generator">generator functions</a> and <a href="#comprehensions">generator expressions</a>.</strong></li>
<li><strong>File objects returned by the <a href="#open">open()</a> function, etc.</strong></li>
</ul><div><h3 id="callable">Callable</h3><ul>
<li><strong>All functions and classes have a call() method, hence are callable.</strong></li>
<li><strong>When this cheatsheet uses <code class="python hljs"><span class="hljs-string">'&lt;function&gt;'</span></code> as an argument, it actually means <code class="python hljs"><span class="hljs-string">'&lt;callable&gt;'</span></code>.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Counter</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self)</span>:</span>
        self.i = <span class="hljs-number">0</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__call__</span><span class="hljs-params">(self)</span>:</span>
        self.i += <span class="hljs-number">1</span>
        <span class="hljs-keyword">return</span> self.i
</code></pre></div></div>




<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>counter = Counter()
<span class="hljs-meta">&gt;&gt;&gt; </span>counter(), counter(), counter()
(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
</code></pre>
<div><h3 id="contextmanager">Context Manager</h3><ul>
<li><strong>Enter() should lock the resources and optionally return an object.</strong></li>
<li><strong>Exit() should release the resources.</strong></li>
<li><strong>Any exception that happens inside the with block is passed to the exit() method.</strong></li>
<li><strong>If it wishes to suppress the exception it must return a true value.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyOpen</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, filename)</span>:</span>
        self.filename = filename
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__enter__</span><span class="hljs-params">(self)</span>:</span>
        self.file = open(self.filename)
        <span class="hljs-keyword">return</span> self.file
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__exit__</span><span class="hljs-params">(self, exc_type, exception, traceback)</span>:</span>
        self.file.close()
</code></pre></div>


<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">with</span> open(<span class="hljs-string">'test.txt'</span>, <span class="hljs-string">'w'</span>) <span class="hljs-keyword">as</span> file:
<span class="hljs-meta">... </span>    file.write(<span class="hljs-string">'Hello World!'</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">with</span> MyOpen(<span class="hljs-string">'test.txt'</span>) <span class="hljs-keyword">as</span> file:
<span class="hljs-meta">... </span>    print(file.read())
Hello World!
</code></pre>
<div><h2 id="iterableducktypes"><a href="#iterableducktypes" name="iterableducktypes">#</a>Iterable Duck Types</h2><div><h3 id="iterable">Iterable</h3><ul>
<li><strong>Only required method is iter(). It should return an iterator of object's items.</strong></li>
<li><strong>Contains() automatically works on any object that has iter() defined.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyIterable</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
        self.a = a
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__iter__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> iter(self.a)
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__contains__</span><span class="hljs-params">(self, el)</span>:</span>
        <span class="hljs-keyword">return</span> el <span class="hljs-keyword">in</span> self.a
</code></pre></div></div>



<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>obj = MyIterable([<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>])
<span class="hljs-meta">&gt;&gt;&gt; </span>[el <span class="hljs-keyword">for</span> el <span class="hljs-keyword">in</span> obj]
[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]
<span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-number">1</span> <span class="hljs-keyword">in</span> obj
<span class="hljs-keyword">True</span>
</code></pre>
<div><h3 id="collection">Collection</h3><ul>
<li><strong>Only required methods are iter() and len().</strong></li>
<li><strong>This cheatsheet actually means <code class="python hljs"><span class="hljs-string">'&lt;iterable&gt;'</span></code> when it uses <code class="python hljs"><span class="hljs-string">'&lt;collection&gt;'</span></code>.</strong></li>
<li><strong>I chose not to use the name 'iterable' because it sounds scarier and more vague than 'collection'.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyCollection</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
        self.a = a
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__iter__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> iter(self.a)
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__contains__</span><span class="hljs-params">(self, el)</span>:</span>
        <span class="hljs-keyword">return</span> el <span class="hljs-keyword">in</span> self.a
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__len__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> len(self.a)
</code></pre></div>


<div><h3 id="sequence">Sequence</h3><ul>
<li><strong>Only required methods are len() and getitem().</strong></li>
<li><strong>Getitem() should return an item at index or raise IndexError.</strong></li>
<li><strong>Iter() and contains() automatically work on any object that has getitem() defined.</strong></li>
<li><strong>Reversed() automatically works on any object that has len() and getitem() defined.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MySequence</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
        self.a = a
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__iter__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> iter(self.a)
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__contains__</span><span class="hljs-params">(self, el)</span>:</span>
        <span class="hljs-keyword">return</span> el <span class="hljs-keyword">in</span> self.a
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__len__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> len(self.a)
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__getitem__</span><span class="hljs-params">(self, i)</span>:</span>
        <span class="hljs-keyword">return</span> self.a[i]
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__reversed__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> reversed(self.a)
</code></pre></div>


<div><h3 id="abcsequence">ABC Sequence</h3><ul>
<li><strong>It's a richer interface than the basic sequence.</strong></li>
<li><strong>Extending it generates iter(), contains(), reversed(), index() and count().</strong></li>
<li><strong>Unlike <code class="python hljs"><span class="hljs-string">'abc.Iterable'</span></code> and <code class="python hljs"><span class="hljs-string">'abc.Collection'</span></code>, it is not a duck type. That is why <code class="python hljs"><span class="hljs-string">'issubclass(MySequence, abc.Sequence)'</span></code> would return False even if MySequence had all the methods defined.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> abc

<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyAbcSequence</span><span class="hljs-params">(abc.Sequence)</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, a)</span>:</span>
        self.a = a
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__len__</span><span class="hljs-params">(self)</span>:</span>
        <span class="hljs-keyword">return</span> len(self.a)
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__getitem__</span><span class="hljs-params">(self, i)</span>:</span>
        <span class="hljs-keyword">return</span> self.a[i]
</code></pre></div>


<div><h4 id="tableofrequiredandautomaticallyavailablespecialmethods">Table of required and automatically available special methods:</h4><pre><code class="text language-text">┏━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━┓
┃            │  Iterable  │ Collection │  Sequence  │ abc.Sequence ┃
┠────────────┼────────────┼────────────┼────────────┼──────────────┨
┃ iter()     │     !      │     !      │     ✓      │      ✓       ┃
┃ contains() │     ✓      │     ✓      │     ✓      │      ✓       ┃
┃ len()      │            │     !      │     !      │      !       ┃
┃ getitem()  │            │            │     !      │      !       ┃
┃ reversed() │            │            │     ✓      │      ✓       ┃
┃ index()    │            │            │            │      ✓       ┃
┃ count()    │            │            │            │      ✓       ┃
┗━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━━━┛
</code></pre></div>

<ul>
<li><strong>Other ABCs that generate missing methods are: MutableSequence, Set, MutableSet, Mapping and MutableMapping.</strong></li>
<li><strong>Names of their required methods are stored in <code class="python hljs"><span class="hljs-string">'&lt;abc&gt;.__abstractmethods__'</span></code>.</strong></li>
</ul>
<div><h2 id="enum"><a href="#enum" name="enum">#</a>Enum</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> enum <span class="hljs-keyword">import</span> Enum, auto

<span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">enum_name</span>&gt;<span class="hljs-params">(Enum)</span>:</span>
    &lt;member_name_1&gt; = &lt;value_1&gt;
    &lt;member_name_2&gt; = &lt;value_2_a&gt;, &lt;value_2_b&gt;
    &lt;member_name_3&gt; = auto()
</code></pre></div>

<ul>
<li><strong>If there are no numeric values before auto(), it returns 1.</strong></li>
<li><strong>Otherwise it returns an increment of the last numeric value.</strong></li>
</ul>
<pre><code class="python language-python hljs">&lt;member&gt; = &lt;enum&gt;.&lt;member_name&gt;                 <span class="hljs-comment"># Returns a member.</span>
&lt;member&gt; = &lt;enum&gt;[<span class="hljs-string">'&lt;member_name&gt;'</span>]              <span class="hljs-comment"># Returns a member or raises KeyError.</span>
&lt;member&gt; = &lt;enum&gt;(&lt;value&gt;)                      <span class="hljs-comment"># Returns a member or raises ValueError.</span>
&lt;str&gt;    = &lt;member&gt;.name                        <span class="hljs-comment"># Returns member's name.</span>
&lt;obj&gt;    = &lt;member&gt;.value                       <span class="hljs-comment"># Returns member's value.</span>
</code></pre>
<pre><code class="python language-python hljs">list_of_members = list(&lt;enum&gt;)
member_names    = [a.name <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> &lt;enum&gt;]
member_values   = [a.value <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> &lt;enum&gt;]
random_member   = random.choice(list(&lt;enum&gt;))
</code></pre>
<pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_next_member</span><span class="hljs-params">(member)</span>:</span>
    members = list(member.__class__)
    index   = (members.index(member) + <span class="hljs-number">1</span>) % len(members)
    <span class="hljs-keyword">return</span> members[index]
</code></pre>
<div><h3 id="inline-2">Inline</h3><pre><code class="python language-python hljs">Cutlery = Enum(<span class="hljs-string">'Cutlery'</span>, <span class="hljs-string">'fork knife spoon'</span>)
Cutlery = Enum(<span class="hljs-string">'Cutlery'</span>, [<span class="hljs-string">'fork'</span>, <span class="hljs-string">'knife'</span>, <span class="hljs-string">'spoon'</span>])
Cutlery = Enum(<span class="hljs-string">'Cutlery'</span>, {<span class="hljs-string">'fork'</span>: <span class="hljs-number">1</span>, <span class="hljs-string">'knife'</span>: <span class="hljs-number">2</span>, <span class="hljs-string">'spoon'</span>: <span class="hljs-number">3</span>})
</code></pre></div>

<div><h4 id="userdefinedfunctionscannotbevaluessotheymustbewrapped">User-defined functions cannot be values, so they must be wrapped:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> functools <span class="hljs-keyword">import</span> partial
LogicOp = Enum(<span class="hljs-string">'LogicOp'</span>, {<span class="hljs-string">'AND'</span>: partial(<span class="hljs-keyword">lambda</span> l, r: l <span class="hljs-keyword">and</span> r),
                           <span class="hljs-string">'OR'</span> : partial(<span class="hljs-keyword">lambda</span> l, r: l <span class="hljs-keyword">or</span> r)})
</code></pre></div>

<ul>
<li><strong>Another solution in this particular case is to use built-in functions and_() and or_() from the module <a href="#operator">operator</a>.</strong></li>
</ul>
<div><h2 id="exceptions"><a href="#exceptions" name="exceptions">#</a>Exceptions</h2><div><h3 id="basicexample">Basic Example</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">try</span>:
    &lt;code&gt;
<span class="hljs-keyword">except</span> &lt;exception&gt;:
    &lt;code&gt;
</code></pre></div></div>


<div><h3 id="complexexample">Complex Example</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">try</span>:
    &lt;code_1&gt;
<span class="hljs-keyword">except</span> &lt;exception_a&gt;:
    &lt;code_2_a&gt;
<span class="hljs-keyword">except</span> &lt;exception_b&gt;:
    &lt;code_2_b&gt;
<span class="hljs-keyword">else</span>:
    &lt;code_2_c&gt;
<span class="hljs-keyword">finally</span>:
    &lt;code_3&gt;
</code></pre></div>

<ul>
<li><strong>Code inside the <code class="python hljs"><span class="hljs-string">'else'</span></code> block will only be executed if <code class="python hljs"><span class="hljs-string">'try'</span></code> block had no exception.</strong></li>
<li><strong>Code inside the <code class="python hljs"><span class="hljs-string">'finally'</span></code> block will always be executed.</strong></li>
</ul>
<div><h3 id="catchingexceptions">Catching Exceptions</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">except</span> &lt;exception&gt;:
<span class="hljs-keyword">except</span> &lt;exception&gt; <span class="hljs-keyword">as</span> &lt;name&gt;:
<span class="hljs-keyword">except</span> (&lt;exception&gt;, [...]):
<span class="hljs-keyword">except</span> (&lt;exception&gt;, [...]) <span class="hljs-keyword">as</span> &lt;name&gt;:
</code></pre></div>

<ul>
<li><strong>Also catches subclasses of the exception.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'traceback.print_exc()'</span></code> to print the error message to stderr.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'print(&lt;name&gt;)'</span></code> to print just the cause of the exception (its arguments).</strong></li>
</ul>
<div><h3 id="raisingexceptions">Raising Exceptions</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">raise</span> &lt;exception&gt;
<span class="hljs-keyword">raise</span> &lt;exception&gt;()
<span class="hljs-keyword">raise</span> &lt;exception&gt;(&lt;el&gt; [, ...])
</code></pre></div>

<div><h4 id="reraisingcaughtexception">Re-raising caught exception:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">except</span> &lt;exception&gt; <span class="hljs-keyword">as</span> &lt;name&gt;:
    ...
    <span class="hljs-keyword">raise</span>
</code></pre></div>

<div><h3 id="exceptionobject">Exception Object</h3><pre><code class="python language-python hljs">arguments = &lt;name&gt;.args
exc_type  = &lt;name&gt;.__class__
filename  = &lt;name&gt;.__traceback__.tb_frame.f_code.co_filename
func_name = &lt;name&gt;.__traceback__.tb_frame.f_code.co_name
line      = linecache.getline(filename, &lt;name&gt;.__traceback__.tb_lineno)
error_msg = <span class="hljs-string">''</span>.join(traceback.format_exception(exc_type, &lt;name&gt;, &lt;name&gt;.__traceback__))
</code></pre></div>

<div><h3 id="builtinexceptions">Built-in Exceptions</h3><pre><code class="text language-text">BaseException
 ├── SystemExit                   <span class="hljs-comment"># Raised by the sys.exit() function.</span>
 ├── KeyboardInterrupt            <span class="hljs-comment"># Raised when the user hits the interrupt key (ctrl-c).</span>
 └── Exception                    <span class="hljs-comment"># User-defined exceptions should be derived from this class.</span>
      ├── ArithmeticError         <span class="hljs-comment"># Base class for arithmetic errors.</span>
      │    └── ZeroDivisionError  <span class="hljs-comment"># Raised when dividing by zero.</span>
      ├── AttributeError          <span class="hljs-comment"># Raised when an attribute is missing.</span>
      ├── EOFError                <span class="hljs-comment"># Raised by input() when it hits end-of-file condition.</span>
      ├── LookupError             <span class="hljs-comment"># Raised when a look-up on a collection fails.</span>
      │    ├── IndexError         <span class="hljs-comment"># Raised when a sequence index is out of range.</span>
      │    └── KeyError           <span class="hljs-comment"># Raised when a dictionary key or set element is not found.</span>
      ├── NameError               <span class="hljs-comment"># Raised when a variable name is not found.</span>
      ├── OSError                 <span class="hljs-comment"># Errors such as “file not found” or “disk full” (see Open).</span>
      │    └── FileNotFoundError  <span class="hljs-comment"># When a file or directory is requested but doesn't exist.</span>
      ├── RuntimeError            <span class="hljs-comment"># Raised by errors that don't fall in other categories.</span>
      │    └── RecursionError     <span class="hljs-comment"># Raised when the maximum recursion depth is exceeded.</span>
      ├── StopIteration           <span class="hljs-comment"># Raised by next() when run on an empty iterator.</span>
      ├── TypeError               <span class="hljs-comment"># Raised when an argument is of wrong type.</span>
      └── ValueError              <span class="hljs-comment"># When an argument is of right type but inappropriate value.</span>
           └── UnicodeError       <span class="hljs-comment"># Raised when encoding/decoding strings to/from bytes fails.</span>
</code></pre></div>

<div><h4 id="collectionsandtheirexceptions">Collections and their exceptions:</h4><pre><code class="text language-text">┏━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┓
┃           │    list    │    dict    │    set     ┃
┠───────────┼────────────┼────────────┼────────────┨
┃ getitem() │ IndexError │  KeyError  │            ┃
┃ pop()     │ IndexError │  KeyError  │  KeyError  ┃
┃ remove()  │ ValueError │            │  KeyError  ┃
┃ index()   │ ValueError │            │            ┃
┗━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┛
</code></pre></div>

<div><h4 id="usefulbuiltinexceptions">Useful built-in exceptions:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">raise</span> TypeError(<span class="hljs-string">'Argument is of wrong type!'</span>)
<span class="hljs-keyword">raise</span> ValueError(<span class="hljs-string">'Argument is of right type but inappropriate value!'</span>)
<span class="hljs-keyword">raise</span> RuntimeError(<span class="hljs-string">'None of above!'</span>)
</code></pre></div>

<div><h3 id="userdefinedexceptions">User-defined Exceptions</h3><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyError</span><span class="hljs-params">(Exception)</span>:</span>
    <span class="hljs-keyword">pass</span>

<span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyInputError</span><span class="hljs-params">(MyError)</span>:</span>
    <span class="hljs-keyword">pass</span>
</code></pre></div>

<div><h2 id="exit"><a href="#exit" name="exit">#</a>Exit</h2><p><strong>Exits the interpreter by raising SystemExit exception.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> sys
sys.exit()                        <span class="hljs-comment"># Exits with exit code 0 (success).</span>
sys.exit(&lt;el&gt;)                    <span class="hljs-comment"># Prints to stderr and exits with 1.</span>
sys.exit(&lt;int&gt;)                   <span class="hljs-comment"># Exits with passed exit code.</span>
</code></pre></div>


<div class="pagebreak"></div><div><h2 id="print"><a href="#print" name="print">#</a>Print</h2><pre><code class="python language-python hljs">print(&lt;el_1&gt;, ..., sep=<span class="hljs-string">' '</span>, end=<span class="hljs-string">'\n'</span>, file=sys.stdout, flush=<span class="hljs-keyword">False</span>)
</code></pre></div>

<ul>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'file=sys.stderr'</span></code> for messages about errors.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'flush=True'</span></code> to forcibly flush the stream.</strong></li>
</ul>
<div><h3 id="prettyprint">Pretty Print</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> pprint <span class="hljs-keyword">import</span> pprint
pprint(&lt;collection&gt;, width=<span class="hljs-number">80</span>, depth=<span class="hljs-keyword">None</span>, compact=<span class="hljs-keyword">False</span>, sort_dicts=<span class="hljs-keyword">True</span>)
</code></pre></div>

<ul>
<li><strong>Levels deeper than 'depth' get replaced by '…'.</strong></li>
</ul>
<div><h2 id="input"><a href="#input" name="input">#</a>Input</h2><p><strong>Reads a line from user input or pipe if present.</strong></p><pre><code class="python language-python hljs">&lt;str&gt; = input(prompt=<span class="hljs-keyword">None</span>)
</code></pre></div>


<ul>
<li><strong>Trailing newline gets stripped.</strong></li>
<li><strong>Prompt string is printed to the standard output before reading input.</strong></li>
<li><strong>Raises EOFError when user hits EOF (ctrl-d/z) or input stream gets exhausted.</strong></li>
</ul>
<div><h2 id="commandlinearguments"><a href="#commandlinearguments" name="commandlinearguments">#</a>Command Line Arguments</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> sys
script_name = sys.argv[<span class="hljs-number">0</span>]
arguments   = sys.argv[<span class="hljs-number">1</span>:]
</code></pre></div>

<div><h3 id="argumentparser">Argument Parser</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> argparse <span class="hljs-keyword">import</span> ArgumentParser, FileType
p = ArgumentParser(description=&lt;str&gt;)
p.add_argument(<span class="hljs-string">'-&lt;short_name&gt;'</span>, <span class="hljs-string">'--&lt;name&gt;'</span>, action=<span class="hljs-string">'store_true'</span>)  <span class="hljs-comment"># Flag</span>
p.add_argument(<span class="hljs-string">'-&lt;short_name&gt;'</span>, <span class="hljs-string">'--&lt;name&gt;'</span>, type=&lt;type&gt;)          <span class="hljs-comment"># Option</span>
p.add_argument(<span class="hljs-string">'&lt;name&gt;'</span>, type=&lt;type&gt;, nargs=<span class="hljs-number">1</span>)                    <span class="hljs-comment"># First argument</span>
p.add_argument(<span class="hljs-string">'&lt;name&gt;'</span>, type=&lt;type&gt;, nargs=<span class="hljs-string">'+'</span>)                  <span class="hljs-comment"># Remaining arguments</span>
p.add_argument(<span class="hljs-string">'&lt;name&gt;'</span>, type=&lt;type&gt;, nargs=<span class="hljs-string">'*'</span>)                  <span class="hljs-comment"># Optional arguments</span>
args  = p.parse_args()                                            <span class="hljs-comment"># Exits on error.</span>
value = args.&lt;name&gt;
</code></pre></div>

<ul>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'help=&lt;str&gt;'</span></code> to set argument description.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'default=&lt;el&gt;'</span></code> to set the default value.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'type=FileType(&lt;mode&gt;)'</span></code> for files.</strong></li>
</ul>
<div><h2 id="open"><a href="#open" name="open">#</a>Open</h2><p><strong>Opens the file and returns a corresponding file object.</strong></p><pre><code class="python language-python hljs">&lt;file&gt; = open(&lt;path&gt;, mode=<span class="hljs-string">'r'</span>, encoding=<span class="hljs-keyword">None</span>, newline=<span class="hljs-keyword">None</span>)
</code></pre></div>


<ul>
<li><strong><code class="python hljs"><span class="hljs-string">'encoding=None'</span></code> means that the default encoding is used, which is platform dependent. Best practice is to use <code class="python hljs"><span class="hljs-string">'encoding="utf-8"'</span></code> whenever possible.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'newline=None'</span></code> means all different end of line combinations are converted to '\n' on read, while on write all '\n' characters are converted to system's default line separator.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'newline=""'</span></code> means no conversions take place, but input is still broken into chunks by readline() and readlines() on either '\n', '\r' or '\r\n'.</strong></li>
</ul>
<div><h3 id="modes">Modes</h3><ul>
<li><strong><code class="python hljs"><span class="hljs-string">'r'</span></code>  - Read (default).</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'w'</span></code>  - Write (truncate).</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'x'</span></code>  - Write or fail if the file already exists.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'a'</span></code>  - Append.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'w+'</span></code> - Read and write (truncate).</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'r+'</span></code> - Read and write from the start.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'a+'</span></code> - Read and write from the end.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'t'</span></code>  - Text mode (default).</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'b'</span></code>  - Binary mode.</strong></li>
</ul><div><h3 id="exceptions-1">Exceptions</h3><ul>
<li><strong><code class="python hljs"><span class="hljs-string">'FileNotFoundError'</span></code> can be raised when reading with <code class="python hljs"><span class="hljs-string">'r'</span></code> or <code class="python hljs"><span class="hljs-string">'r+'</span></code>.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'FileExistsError'</span></code> can be raised when writing with <code class="python hljs"><span class="hljs-string">'x'</span></code>.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'IsADirectoryError'</span></code> and <code class="python hljs"><span class="hljs-string">'PermissionError'</span></code> can be raised by any.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'OSError'</span></code> is the parent class of all listed exceptions.</strong></li>
</ul><div><h3 id="fileobject">File Object</h3><pre><code class="python language-python hljs">&lt;file&gt;.seek(<span class="hljs-number">0</span>)                      <span class="hljs-comment"># Moves to the start of the file.</span>
&lt;file&gt;.seek(offset)                 <span class="hljs-comment"># Moves 'offset' chars/bytes from the start.</span>
&lt;file&gt;.seek(<span class="hljs-number">0</span>, <span class="hljs-number">2</span>)                   <span class="hljs-comment"># Moves to the end of the file.</span>
&lt;bin_file&gt;.seek(±offset, &lt;anchor&gt;)  <span class="hljs-comment"># Anchor: 0 start, 1 current position, 2 end.</span>
</code></pre></div></div></div>





<pre><code class="python language-python hljs">&lt;str/bytes&gt; = &lt;file&gt;.read(size=<span class="hljs-number">-1</span>)  <span class="hljs-comment"># Reads 'size' chars/bytes or until EOF.</span>
&lt;str/bytes&gt; = &lt;file&gt;.readline()     <span class="hljs-comment"># Returns a line or empty string/bytes on EOF.</span>
&lt;list&gt;      = &lt;file&gt;.readlines()    <span class="hljs-comment"># Returns a list of remaining lines.</span>
&lt;str/bytes&gt; = next(&lt;file&gt;)          <span class="hljs-comment"># Returns a line using buffer. Do not mix.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;file&gt;.write(&lt;str/bytes&gt;)           <span class="hljs-comment"># Writes a string or bytes object.</span>
&lt;file&gt;.writelines(&lt;collection&gt;)     <span class="hljs-comment"># Writes a coll. of strings or bytes objects.</span>
&lt;file&gt;.flush()                      <span class="hljs-comment"># Flushes write buffer.</span>
</code></pre>
<ul>
<li><strong>Methods do not add or strip trailing newlines, even writelines().</strong></li>
</ul>
<div><h3 id="readtextfromfile">Read Text from File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_file</span><span class="hljs-params">(filename)</span>:</span>
    <span class="hljs-keyword">with</span> open(filename, encoding=<span class="hljs-string">'utf-8'</span>) <span class="hljs-keyword">as</span> file:
        <span class="hljs-keyword">return</span> file.readlines()
</code></pre></div>

<div><h3 id="writetexttofile">Write Text to File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_file</span><span class="hljs-params">(filename, text)</span>:</span>
    <span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'w'</span>, encoding=<span class="hljs-string">'utf-8'</span>) <span class="hljs-keyword">as</span> file:
        file.write(text)
</code></pre></div>

<div><h2 id="path"><a href="#path" name="path">#</a>Path</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> os <span class="hljs-keyword">import</span> getcwd, path, listdir
<span class="hljs-keyword">from</span> glob <span class="hljs-keyword">import</span> glob
</code></pre></div>

<pre><code class="python language-python hljs">&lt;str&gt;  = getcwd()                   <span class="hljs-comment"># Returns the current working directory.</span>
&lt;str&gt;  = path.join(&lt;path&gt;, ...)     <span class="hljs-comment"># Joins two or more pathname components.</span>
&lt;str&gt;  = path.abspath(&lt;path&gt;)       <span class="hljs-comment"># Returns absolute path.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;str&gt;  = path.basename(&lt;path&gt;)      <span class="hljs-comment"># Returns final component of the path.</span>
&lt;str&gt;  = path.dirname(&lt;path&gt;)       <span class="hljs-comment"># Returns path without the final component.</span>
&lt;tup.&gt; = path.splitext(&lt;path&gt;)      <span class="hljs-comment"># Splits on last period of the final component.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;list&gt; = listdir(path=<span class="hljs-string">'.'</span>)          <span class="hljs-comment"># Returns filenames located at path.</span>
&lt;list&gt; = glob(<span class="hljs-string">'&lt;pattern&gt;'</span>)          <span class="hljs-comment"># Returns paths matching the wildcard pattern.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;bool&gt; = path.exists(&lt;path&gt;)        <span class="hljs-comment"># Or: &lt;Path&gt;.exists()</span>
&lt;bool&gt; = path.isfile(&lt;path&gt;)        <span class="hljs-comment"># Or: &lt;DirEntry/Path&gt;.is_file()</span>
&lt;bool&gt; = path.isdir(&lt;path&gt;)         <span class="hljs-comment"># Or: &lt;DirEntry/Path&gt;.is_dir()</span>
</code></pre>
<div><h3 id="direntry">DirEntry</h3><p><strong>Using scandir() instead of listdir() can significantly increase the performance of code that also needs file type information.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> os <span class="hljs-keyword">import</span> scandir
</code></pre></div>


<pre><code class="python language-python hljs">&lt;iter&gt; = scandir(path=<span class="hljs-string">'.'</span>)          <span class="hljs-comment"># Returns DirEntry objects located at path.</span>
&lt;str&gt;  = &lt;DirEntry&gt;.path            <span class="hljs-comment"># Returns whole path as a string.</span>
&lt;str&gt;  = &lt;DirEntry&gt;.name            <span class="hljs-comment"># Returns final component as a string.</span>
&lt;file&gt; = open(&lt;DirEntry&gt;)           <span class="hljs-comment"># Opens the file and returns file object.</span>
</code></pre>
<div><h3 id="pathobject">Path Object</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> pathlib <span class="hljs-keyword">import</span> Path
</code></pre></div>

<pre><code class="python language-python hljs">&lt;Path&gt; = Path(&lt;path&gt; [, ...])       <span class="hljs-comment"># Accepts strings, Paths and DirEntry objects.</span>
&lt;Path&gt; = &lt;path&gt; / &lt;path&gt; [/ ...]    <span class="hljs-comment"># One of the paths must be a Path object.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;Path&gt; = Path()                     <span class="hljs-comment"># Returns relative cwd. Also Path('.').</span>
&lt;Path&gt; = Path.cwd()                 <span class="hljs-comment"># Returns absolute cwd. Also Path().resolve().</span>
&lt;Path&gt; = Path.home()                <span class="hljs-comment"># Returns user's home directory.</span>
&lt;Path&gt; = Path(__file__).resolve()   <span class="hljs-comment"># Returns script's path if cwd wasn't changed.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;Path&gt; = &lt;Path&gt;.parent              <span class="hljs-comment"># Returns Path without final component.</span>
&lt;str&gt;  = &lt;Path&gt;.name                <span class="hljs-comment"># Returns final component as a string.</span>
&lt;str&gt;  = &lt;Path&gt;.stem                <span class="hljs-comment"># Returns final component without extension.</span>
&lt;str&gt;  = &lt;Path&gt;.suffix              <span class="hljs-comment"># Returns final component's extension.</span>
&lt;tup.&gt; = &lt;Path&gt;.parts               <span class="hljs-comment"># Returns all components as strings.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;iter&gt; = &lt;Path&gt;.iterdir()           <span class="hljs-comment"># Returns dir contents as Path objects.</span>
&lt;iter&gt; = &lt;Path&gt;.glob(<span class="hljs-string">'&lt;pattern&gt;'</span>)   <span class="hljs-comment"># Returns Paths matching the wildcard pattern.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;str&gt;  = str(&lt;Path&gt;)                <span class="hljs-comment"># Returns path as a string.</span>
&lt;file&gt; = open(&lt;Path&gt;)               <span class="hljs-comment"># Opens the file and returns file object.</span>
</code></pre>
<div><h2 id="oscommands"><a href="#oscommands" name="oscommands">#</a>OS Commands</h2><div><h3 id="filesanddirectories">Files and Directories</h3><ul>
<li><strong>Paths can be either strings, Paths or DirEntry objects.</strong></li>
<li><strong>Functions report OS related errors by raising either OSError or one of its <a href="#exceptions-1">subclasses</a>.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> os, shutil
</code></pre></div></div>



<pre><code class="python language-python hljs">os.chdir(&lt;path&gt;)                    <span class="hljs-comment"># Changes the current working directory.</span>
os.mkdir(&lt;path&gt;, mode=<span class="hljs-number">0o777</span>)        <span class="hljs-comment"># Creates a directory. Mode is in octal.</span>
</code></pre>
<pre><code class="python language-python hljs">shutil.copy(from, to)               <span class="hljs-comment"># Copies the file. 'to' can exist or be a dir.</span>
shutil.copytree(from, to)           <span class="hljs-comment"># Copies the directory. 'to' must not exist.</span>
</code></pre>
<pre><code class="python language-python hljs">os.rename(from, to)                 <span class="hljs-comment"># Renames/moves the file or directory.</span>
os.replace(from, to)                <span class="hljs-comment"># Same, but overwrites 'to' if it exists.</span>
</code></pre>
<pre><code class="python language-python hljs">os.remove(&lt;path&gt;)                   <span class="hljs-comment"># Deletes the file.</span>
os.rmdir(&lt;path&gt;)                    <span class="hljs-comment"># Deletes the empty directory.</span>
shutil.rmtree(&lt;path&gt;)               <span class="hljs-comment"># Deletes the directory.</span>
</code></pre>
<div><h3 id="shellcommands">Shell Commands</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> os
&lt;str&gt; = os.popen(<span class="hljs-string">'&lt;shell_command&gt;'</span>).read()
</code></pre></div>

<div><h4 id="sends11tothebasiccalculatorandcapturesitsoutput">Sends '1 + 1' to the basic calculator and captures its output:</h4><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> subprocess <span class="hljs-keyword">import</span> run
<span class="hljs-meta">&gt;&gt;&gt; </span>run(<span class="hljs-string">'bc'</span>, input=<span class="hljs-string">'1 + 1\n'</span>, capture_output=<span class="hljs-keyword">True</span>, encoding=<span class="hljs-string">'utf-8'</span>)
CompletedProcess(args=<span class="hljs-string">'bc'</span>, returncode=<span class="hljs-number">0</span>, stdout=<span class="hljs-string">'2\n'</span>, stderr=<span class="hljs-string">''</span>)
</code></pre></div>

<div><h4 id="sendstestintothebasiccalculatorrunninginstandardmodeandsavesitsoutputtotestout">Sends test.in to the basic calculator running in standard mode and saves its output to test.out:</h4><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> shlex <span class="hljs-keyword">import</span> split
<span class="hljs-meta">&gt;&gt;&gt; </span>os.popen(<span class="hljs-string">'echo 1 + 1 &gt; test.in'</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>run(split(<span class="hljs-string">'bc -s'</span>), stdin=open(<span class="hljs-string">'test.in'</span>), stdout=open(<span class="hljs-string">'test.out'</span>, <span class="hljs-string">'w'</span>))
CompletedProcess(args=[<span class="hljs-string">'bc'</span>, <span class="hljs-string">'-s'</span>], returncode=<span class="hljs-number">0</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>open(<span class="hljs-string">'test.out'</span>).read()
<span class="hljs-string">'2\n'</span>
</code></pre></div>

<div><h2 id="json"><a href="#json" name="json">#</a>JSON</h2><p><strong>Text file format for storing collections of strings and numbers.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> json
&lt;str&gt;    = json.dumps(&lt;object&gt;, ensure_ascii=<span class="hljs-keyword">True</span>, indent=<span class="hljs-keyword">None</span>)
&lt;object&gt; = json.loads(&lt;str&gt;)
</code></pre></div>


<div><h3 id="readobjectfromjsonfile">Read Object from JSON File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_json_file</span><span class="hljs-params">(filename)</span>:</span>
    <span class="hljs-keyword">with</span> open(filename, encoding=<span class="hljs-string">'utf-8'</span>) <span class="hljs-keyword">as</span> file:
        <span class="hljs-keyword">return</span> json.load(file)
</code></pre></div>

<div><h3 id="writeobjecttojsonfile">Write Object to JSON File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_json_file</span><span class="hljs-params">(filename, an_object)</span>:</span>
    <span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'w'</span>, encoding=<span class="hljs-string">'utf-8'</span>) <span class="hljs-keyword">as</span> file:
        json.dump(an_object, file, ensure_ascii=<span class="hljs-keyword">False</span>, indent=<span class="hljs-number">2</span>)
</code></pre></div>

<div><h2 id="pickle"><a href="#pickle" name="pickle">#</a>Pickle</h2><p><strong>Binary file format for storing objects.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> pickle
&lt;bytes&gt;  = pickle.dumps(&lt;object&gt;)
&lt;object&gt; = pickle.loads(&lt;bytes&gt;)
</code></pre></div>


<div><h3 id="readobjectfromfile">Read Object from File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_pickle_file</span><span class="hljs-params">(filename)</span>:</span>
    <span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'rb'</span>) <span class="hljs-keyword">as</span> file:
        <span class="hljs-keyword">return</span> pickle.load(file)
</code></pre></div>

<div><h3 id="writeobjecttofile">Write Object to File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_pickle_file</span><span class="hljs-params">(filename, an_object)</span>:</span>
    <span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'wb'</span>) <span class="hljs-keyword">as</span> file:
        pickle.dump(an_object, file)
</code></pre></div>

<div><h2 id="csv"><a href="#csv" name="csv">#</a>CSV</h2><p><strong>Text file format for storing spreadsheets.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> csv
</code></pre></div>


<div><h3 id="read">Read</h3><pre><code class="python language-python hljs">&lt;reader&gt; = csv.reader(&lt;file&gt;)       <span class="hljs-comment"># Also: `dialect='excel', delimiter=','`.</span>
&lt;list&gt;   = next(&lt;reader&gt;)           <span class="hljs-comment"># Returns next row as a list of strings.</span>
&lt;list&gt;   = list(&lt;reader&gt;)           <span class="hljs-comment"># Returns list of remaining rows.</span>
</code></pre></div>

<ul>
<li><strong>File must be opened with <code class="python hljs"><span class="hljs-string">'newline=""'</span></code> argument, or newlines embedded inside quoted fields will not be interpreted correctly!</strong></li>
</ul>
<div><h3 id="write">Write</h3><pre><code class="python language-python hljs">&lt;writer&gt; = csv.writer(&lt;file&gt;)       <span class="hljs-comment"># Also: `dialect='excel', delimiter=','`.</span>
&lt;writer&gt;.writerow(&lt;collection&gt;)     <span class="hljs-comment"># Encodes objects using `str(&lt;el&gt;)`.</span>
&lt;writer&gt;.writerows(&lt;coll_of_coll&gt;)  <span class="hljs-comment"># Appends multiple rows.</span>
</code></pre></div>

<ul>
<li><strong>File must be opened with <code class="python hljs"><span class="hljs-string">'newline=""'</span></code> argument, or '\r' will be added in front of every '\n' on platforms that use '\r\n' line endings!</strong></li>
</ul>
<div><h3 id="parameters">Parameters</h3><ul>
<li><strong><code class="python hljs"><span class="hljs-string">'dialect'</span></code> - Master parameter that sets the default values.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'delimiter'</span></code> - A one-character string used to separate fields.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'quotechar'</span></code> - Character for quoting fields that contain special characters.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'doublequote'</span></code> - Whether quotechars inside fields get doubled or escaped.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'skipinitialspace'</span></code> - Whether whitespace after delimiter gets stripped.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'lineterminator'</span></code> - Specifies how writer terminates rows.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'quoting'</span></code> - Controls the amount of quoting: 0 - as necessary, 1 - all.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'escapechar'</span></code> - Character for escaping 'quotechar' if 'doublequote' is False.</strong></li>
</ul><div><h3 id="dialects">Dialects</h3><pre><code class="text language-text">┏━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━┓
┃                  │     excel    │   excel-tab  │     unix     ┃
┠──────────────────┼──────────────┼──────────────┼──────────────┨
┃ delimiter        │       ','    │      '\t'    │       ','    ┃
┃ quotechar        │       '"'    │       '"'    │       '"'    ┃
┃ doublequote      │      True    │      True    │      True    ┃
┃ skipinitialspace │     False    │     False    │     False    ┃
┃ lineterminator   │    '\r\n'    │    '\r\n'    │      '\n'    ┃
┃ quoting          │         0    │         0    │         1    ┃
┃ escapechar       │      None    │      None    │      None    ┃
┗━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━┛
</code></pre></div></div>



<div><h3 id="readrowsfromcsvfile">Read Rows from CSV File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_csv_file</span><span class="hljs-params">(filename)</span>:</span>
    <span class="hljs-keyword">with</span> open(filename, encoding=<span class="hljs-string">'utf-8'</span>, newline=<span class="hljs-string">''</span>) <span class="hljs-keyword">as</span> file:
        <span class="hljs-keyword">return</span> list(csv.reader(file))
</code></pre></div>

<div><h3 id="writerowstocsvfile">Write Rows to CSV File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_csv_file</span><span class="hljs-params">(filename, rows)</span>:</span>
    <span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'w'</span>, encoding=<span class="hljs-string">'utf-8'</span>, newline=<span class="hljs-string">''</span>) <span class="hljs-keyword">as</span> file:
        writer = csv.writer(file)
        writer.writerows(rows)
</code></pre></div>

<div><h2 id="sqlite"><a href="#sqlite" name="sqlite">#</a>SQLite</h2><p><strong>Server-less database engine that stores each database into a separate file.</strong></p><div><h3 id="connect">Connect</h3><p><strong>Opens a connection to the database file. Creates a new file if path doesn't exist.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> sqlite3
&lt;conn&gt; = sqlite3.connect(&lt;path&gt;)                <span class="hljs-comment"># Also ':memory:'.</span>
&lt;conn&gt;.close()                                  <span class="hljs-comment"># Closes the connection.</span>
</code></pre></div></div>




<div><h3 id="read-1">Read</h3><p><strong>Returned values can be of type str, int, float, bytes or None.</strong></p><pre><code class="python language-python hljs">&lt;cursor&gt; = &lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>)            <span class="hljs-comment"># Can raise a subclass of sqlite3.Error.</span>
&lt;tuple&gt;  = &lt;cursor&gt;.fetchone()                  <span class="hljs-comment"># Returns next row. Also next(&lt;cursor&gt;).</span>
&lt;list&gt;   = &lt;cursor&gt;.fetchall()                  <span class="hljs-comment"># Returns remaining rows. Also list(&lt;cursor&gt;).</span>
</code></pre></div>


<div><h3 id="write-1">Write</h3><pre><code class="python language-python hljs">&lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>)                       <span class="hljs-comment"># Can raise a subclass of sqlite3.Error.</span>
&lt;conn&gt;.commit()                                 <span class="hljs-comment"># Commits all transactions since last commit.</span>
</code></pre></div>

<div><h4 id="or">Or:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">with</span> &lt;conn&gt;:
    &lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>)
</code></pre></div>

<div><h3 id="placeholders">Placeholders</h3><ul>
<li><strong>Passed values can be of type str, int, float, bytes, None, bool, datetime.date or datetime.datetme.</strong></li>
<li><strong>Bools will be stored and returned as ints and dates as <a href="#encode">ISO formatted strings</a>.</strong></li>
</ul><pre><code class="python language-python hljs">&lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;list/tuple&gt;)         <span class="hljs-comment"># Replaces '?'s in query with values.</span>
&lt;conn&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;dict/namedtuple&gt;)    <span class="hljs-comment"># Replaces ':&lt;key&gt;'s with values.</span>
&lt;conn&gt;.executemany(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;coll_of_above&gt;)  <span class="hljs-comment"># Runs execute() multiple times.</span>
</code></pre></div>


<div><h3 id="example">Example</h3><p><strong>In this example values are not actually saved because <code class="python hljs"><span class="hljs-string">'conn.commit()'</span></code> is omitted!</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>conn = sqlite3.connect(<span class="hljs-string">'test.db'</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>conn.execute(<span class="hljs-string">'create table person (person_id integer primary key, name, height)'</span>)
<span class="hljs-meta">&gt;&gt;&gt; </span>conn.execute(<span class="hljs-string">'insert into person values (null, ?, ?)'</span>, (<span class="hljs-string">'Jean-Luc'</span>, <span class="hljs-number">187</span>)).lastrowid
<span class="hljs-number">1</span>
<span class="hljs-meta">&gt;&gt;&gt; </span>conn.execute(<span class="hljs-string">'select * from person'</span>).fetchall()
[(<span class="hljs-number">1</span>, <span class="hljs-string">'Jean-Luc'</span>, <span class="hljs-number">187</span>)]
</code></pre></div>


<div><h3 id="mysql">MySQL</h3><p><strong>Has a very similar interface, with differences listed below.</strong></p><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install mysql-connector</span>
<span class="hljs-keyword">from</span> mysql <span class="hljs-keyword">import</span> connector
&lt;conn&gt;   = connector.connect(host=&lt;str&gt;, …)     <span class="hljs-comment"># `user=&lt;str&gt;, password=&lt;str&gt;, database=&lt;str&gt;`.</span>
&lt;cursor&gt; = &lt;conn&gt;.cursor()                      <span class="hljs-comment"># Only cursor has execute method.</span>
&lt;cursor&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>)                     <span class="hljs-comment"># Can raise a subclass of connector.Error.</span>
&lt;cursor&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;list/tuple&gt;)       <span class="hljs-comment"># Replaces '%s's in query with values.</span>
&lt;cursor&gt;.execute(<span class="hljs-string">'&lt;query&gt;'</span>, &lt;dict/namedtuple&gt;)  <span class="hljs-comment"># Replaces '%(&lt;key&gt;)s's with values.</span>
</code></pre></div>


<div><h2 id="bytes"><a href="#bytes" name="bytes">#</a>Bytes</h2><p><strong>Bytes object is an immutable sequence of single bytes. Mutable version is called bytearray.</strong></p><pre><code class="python language-python hljs">&lt;bytes&gt; = <span class="hljs-string">b'&lt;str&gt;'</span>                       <span class="hljs-comment"># Only accepts ASCII characters and \x00 - \xff.</span>
&lt;int&gt;   = &lt;bytes&gt;[&lt;index&gt;]               <span class="hljs-comment"># Returns int in range from 0 to 255.</span>
&lt;bytes&gt; = &lt;bytes&gt;[&lt;slice&gt;]               <span class="hljs-comment"># Returns bytes even if it has only one element.</span>
&lt;bytes&gt; = &lt;bytes&gt;.join(&lt;coll_of_bytes&gt;)  <span class="hljs-comment"># Joins elements using bytes object as separator.</span>
</code></pre></div>


<div><h3 id="encode-1">Encode</h3><pre><code class="python language-python hljs">&lt;bytes&gt; = bytes(&lt;coll_of_ints&gt;)          <span class="hljs-comment"># Ints must be in range from 0 to 255.</span>
&lt;bytes&gt; = bytes(&lt;str&gt;, <span class="hljs-string">'utf-8'</span>)          <span class="hljs-comment"># Or: &lt;str&gt;.encode('utf-8')</span>
&lt;bytes&gt; = &lt;int&gt;.to_bytes(n_bytes, …)     <span class="hljs-comment"># `byteorder='big/little', signed=False`.</span>
&lt;bytes&gt; = bytes.fromhex(<span class="hljs-string">'&lt;hex&gt;'</span>)         <span class="hljs-comment"># Hex pairs can be separated by spaces.</span>
</code></pre></div>

<div><h3 id="decode-1">Decode</h3><pre><code class="python language-python hljs">&lt;list&gt;  = list(&lt;bytes&gt;)                  <span class="hljs-comment"># Returns ints in range from 0 to 255.</span>
&lt;str&gt;   = str(&lt;bytes&gt;, <span class="hljs-string">'utf-8'</span>)          <span class="hljs-comment"># Or: &lt;bytes&gt;.decode('utf-8')</span>
&lt;int&gt;   = int.from_bytes(&lt;bytes&gt;, …)     <span class="hljs-comment"># `byteorder='big/little', signed=False`.</span>
<span class="hljs-string">'&lt;hex&gt;'</span> = &lt;bytes&gt;.hex()                  <span class="hljs-comment"># Returns a string of hexadecimal pairs.</span>
</code></pre></div>

<div><h3 id="readbytesfromfile">Read Bytes from File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_bytes</span><span class="hljs-params">(filename)</span>:</span>
    <span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'rb'</span>) <span class="hljs-keyword">as</span> file:
        <span class="hljs-keyword">return</span> file.read()
</code></pre></div>

<div><h3 id="writebytestofile">Write Bytes to File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_bytes</span><span class="hljs-params">(filename, bytes_obj)</span>:</span>
    <span class="hljs-keyword">with</span> open(filename, <span class="hljs-string">'wb'</span>) <span class="hljs-keyword">as</span> file:
        file.write(bytes_obj)
</code></pre></div>

<div><h2 id="struct"><a href="#struct" name="struct">#</a>Struct</h2><ul>
<li><strong>Module that performs conversions between a sequence of numbers and a bytes object.</strong></li>
<li><strong>Machine’s native type sizes and byte order are used by default.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> struct <span class="hljs-keyword">import</span> pack, unpack, iter_unpack
&lt;bytes&gt;  = pack(<span class="hljs-string">'&lt;format&gt;'</span>, &lt;num_1&gt; [, &lt;num_2&gt;, ...])
&lt;tuple&gt;  = unpack(<span class="hljs-string">'&lt;format&gt;'</span>, &lt;bytes&gt;)
&lt;tuples&gt; = iter_unpack(<span class="hljs-string">'&lt;format&gt;'</span>, &lt;bytes&gt;)
</code></pre></div>


<div><h3 id="example-1">Example</h3><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>pack(<span class="hljs-string">'&gt;hhl'</span>, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
<span class="hljs-string">b'\x00\x01\x00\x02\x00\x00\x00\x03'</span>
<span class="hljs-meta">&gt;&gt;&gt; </span>unpack(<span class="hljs-string">'&gt;hhl'</span>, <span class="hljs-string">b'\x00\x01\x00\x02\x00\x00\x00\x03'</span>)
(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>)
</code></pre></div>

<div><h3 id="format-2">Format</h3><div><h4 id="forstandardtypesizesstartformatstringwith">For standard type sizes start format string with:</h4><ul>
<li><strong><code class="python hljs"><span class="hljs-string">'='</span></code> - native byte order (usually little-endian)</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'&lt;'</span></code> - little-endian</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'&gt;'</span></code> - big-endian (also <code class="python hljs"><span class="hljs-string">'!'</span></code>)</strong></li>
</ul></div></div><div><h4 id="integertypesuseacapitalletterforunsignedtypeminimumandstandardsizesareinbrackets">Integer types. Use a capital letter for unsigned type. Minimum and standard sizes are in brackets:</h4><ul>
<li><strong><code class="python hljs"><span class="hljs-string">'x'</span></code> - pad byte</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'b'</span></code> - char (1/1)</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'h'</span></code> - short (2/2)</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'i'</span></code> - int (2/4)</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'l'</span></code> - long (4/4)</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'q'</span></code> - long long (8/8)</strong></li>
</ul></div><div><h4 id="floatingpointtypes">Floating point types:</h4><ul>
<li><strong><code class="python hljs"><span class="hljs-string">'f'</span></code> - float (4/4)</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'d'</span></code> - double (8/8)</strong></li>
</ul></div>






<div><h2 id="array"><a href="#array" name="array">#</a>Array</h2><p><strong>List that can only hold numbers of a predefined type. Available types and their minimum sizes in bytes are listed above. Sizes and byte order are always determined by the system.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> array <span class="hljs-keyword">import</span> array
&lt;array&gt; = array(<span class="hljs-string">'&lt;typecode&gt;'</span>, &lt;collection&gt;)    <span class="hljs-comment"># Array from collection of numbers.</span>
&lt;array&gt; = array(<span class="hljs-string">'&lt;typecode&gt;'</span>, &lt;bytes&gt;)         <span class="hljs-comment"># Array from bytes object.</span>
&lt;array&gt; = array(<span class="hljs-string">'&lt;typecode&gt;'</span>, &lt;array&gt;)         <span class="hljs-comment"># Treats array as a sequence of numbers.</span>
&lt;bytes&gt; = bytes(&lt;array&gt;)                       <span class="hljs-comment"># Or: &lt;array&gt;.tobytes()</span>
</code></pre></div>


<div><h2 id="memoryview"><a href="#memoryview" name="memoryview">#</a>Memory View</h2><ul>
<li><strong>A sequence object that points to the memory of another object.</strong></li>
<li><strong>Each element can reference a single or multiple consecutive bytes, depending on format.</strong></li>
<li><strong>Order and number of elements can be changed with slicing.</strong></li>
</ul><pre><code class="python language-python hljs">&lt;mview&gt; = memoryview(&lt;bytes/bytearray/array&gt;)  <span class="hljs-comment"># Immutable if bytes, else mutable.</span>
&lt;real&gt;  = &lt;mview&gt;[&lt;index&gt;]                     <span class="hljs-comment"># Returns an int or a float.</span>
&lt;mview&gt; = &lt;mview&gt;[&lt;slice&gt;]                     <span class="hljs-comment"># Mview with rearranged elements.</span>
&lt;mview&gt; = &lt;mview&gt;.cast(<span class="hljs-string">'&lt;typecode&gt;'</span>)           <span class="hljs-comment"># Casts memoryview to the new format.</span>
&lt;mview&gt;.release()                              <span class="hljs-comment"># Releases the object's memory buffer.</span>
</code></pre></div>


<div><h3 id="decode-2">Decode</h3><pre><code class="python language-python hljs">&lt;bin_file&gt;.write(&lt;mview&gt;)                      <span class="hljs-comment"># Writes mview to the binary file.</span>
&lt;bytes&gt; = bytes(&lt;mview&gt;)                       <span class="hljs-comment"># Creates a new bytes object.</span>
&lt;bytes&gt; = &lt;bytes&gt;.join(&lt;coll_of_mviews&gt;)       <span class="hljs-comment"># Joins mviews using bytes object as sep.</span>
&lt;array&gt; = array(<span class="hljs-string">'&lt;typecode&gt;'</span>, &lt;mview&gt;)         <span class="hljs-comment"># Treats mview as a sequence of numbers.</span>
</code></pre></div>

<pre><code class="python language-python hljs">&lt;list&gt;  = list(&lt;mview&gt;)                        <span class="hljs-comment"># Returns list of ints or floats.</span>
&lt;str&gt;   = str(&lt;mview&gt;, <span class="hljs-string">'utf-8'</span>)                <span class="hljs-comment"># Treats mview as a bytes object.</span>
&lt;int&gt;   = int.from_bytes(&lt;mview&gt;, …)           <span class="hljs-comment"># `byteorder='big/little', signed=False`.</span>
<span class="hljs-string">'&lt;hex&gt;'</span> = &lt;mview&gt;.hex()                        <span class="hljs-comment"># Treats mview as a bytes object.</span>
</code></pre>
<div><h2 id="deque"><a href="#deque" name="deque">#</a>Deque</h2><p><strong>A thread-safe list with efficient appends and pops from either side. Pronounced "deck".</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> deque
&lt;deque&gt; = deque(&lt;collection&gt;, maxlen=<span class="hljs-keyword">None</span>)
</code></pre></div>


<pre><code class="python language-python hljs">&lt;deque&gt;.appendleft(&lt;el&gt;)                       <span class="hljs-comment"># Opposite element is dropped if full.</span>
&lt;deque&gt;.extendleft(&lt;collection&gt;)               <span class="hljs-comment"># Collection gets reversed.</span>
&lt;el&gt; = &lt;deque&gt;.popleft()                       <span class="hljs-comment"># Raises IndexError if empty.</span>
&lt;deque&gt;.rotate(n=<span class="hljs-number">1</span>)                            <span class="hljs-comment"># Rotates elements to the right.</span>
</code></pre>
<div><h2 id="threading"><a href="#threading" name="threading">#</a>Threading</h2><ul>
<li><strong>CPython interpreter can only run a single thread at a time.</strong></li>
<li><strong>That is why using multiple threads won't result in a faster execution, unless at least one of the threads contains an I/O operation.</strong></li>
</ul><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> threading <span class="hljs-keyword">import</span> Thread, RLock, Semaphore, Event, Barrier
</code></pre></div>


<div><h3 id="thread">Thread</h3><pre><code class="python language-python hljs">&lt;Thread&gt; = Thread(target=&lt;function&gt;)  <span class="hljs-comment"># Use `args=&lt;collection&gt;` to set arguments.</span>
&lt;Thread&gt;.start()                      <span class="hljs-comment"># Starts the thread.</span>
&lt;bool&gt; = &lt;Thread&gt;.is_alive()          <span class="hljs-comment"># Checks if thread has finished executing.</span>
&lt;Thread&gt;.join()                       <span class="hljs-comment"># Waits for thread to finish.</span>
</code></pre></div>

<ul>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'kwargs=&lt;dict&gt;'</span></code> to pass keyword arguments to the function.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'daemon=True'</span></code>, or the program will not be able to exit while the thread is alive.</strong></li>
</ul>
<div><h3 id="lock">Lock</h3><pre><code class="python language-python hljs">&lt;lock&gt; = RLock()                      <span class="hljs-comment"># Lock that can only be released by the owner.</span>
&lt;lock&gt;.acquire()                      <span class="hljs-comment"># Waits for lock to be available.</span>
&lt;lock&gt;.release()                      <span class="hljs-comment"># Makes lock available again.</span>
</code></pre></div>

<div><h4 id="or-1">Or:</h4><pre><code class="python language-python hljs">lock = RLock()
<span class="hljs-keyword">with</span> lock:
    ...
</code></pre></div>

<div><h3 id="semaphoreeventbarrier">Semaphore, Event, Barrier</h3><pre><code class="python language-python hljs">&lt;Semaphore&gt; = Semaphore(value=<span class="hljs-number">1</span>)      <span class="hljs-comment"># Lock that can be acquired 'value' times.</span>
&lt;Event&gt;     = Event()                 <span class="hljs-comment"># Method wait() blocks until set() is called.</span>
&lt;Barrier&gt;   = Barrier(n_times)        <span class="hljs-comment"># Method wait() blocks until it's called 'n_times'.</span>
</code></pre></div>

<div><h3 id="threadpoolexecutor">Thread Pool Executor</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> concurrent.futures <span class="hljs-keyword">import</span> ThreadPoolExecutor
<span class="hljs-keyword">with</span> ThreadPoolExecutor(max_workers=<span class="hljs-keyword">None</span>) <span class="hljs-keyword">as</span> executor:         <span class="hljs-comment"># Does not exit until done.</span>
    &lt;iter&gt;   = executor.map(<span class="hljs-keyword">lambda</span> x: x + <span class="hljs-number">1</span>, range(<span class="hljs-number">3</span>))         <span class="hljs-comment"># (1, 2, 3)</span>
    &lt;iter&gt;   = executor.map(<span class="hljs-keyword">lambda</span> x, y: x + y, <span class="hljs-string">'abc'</span>, <span class="hljs-string">'123'</span>)  <span class="hljs-comment"># ('a1', 'b2', 'c3')</span>
    &lt;Future&gt; = executor.submit(&lt;function&gt; [, &lt;arg_1&gt;, ...])    <span class="hljs-comment"># Also visible outside block.</span>
</code></pre></div>

<div><h4 id="future">Future:</h4><pre><code class="python language-python hljs">&lt;bool&gt; = &lt;Future&gt;.done()              <span class="hljs-comment"># Checks if thread has finished executing.</span>
&lt;obj&gt;  = &lt;Future&gt;.result()            <span class="hljs-comment"># Waits for thread to finish and returns result.</span>
</code></pre></div>

<div><h3 id="queue">Queue</h3><p><strong>A thread-safe FIFO queue. For LIFO queue use LifoQueue.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> queue <span class="hljs-keyword">import</span> Queue
&lt;Queue&gt; = Queue(maxsize=<span class="hljs-number">0</span>)
</code></pre></div>


<pre><code class="python language-python hljs">&lt;Queue&gt;.put(&lt;el&gt;)                     <span class="hljs-comment"># Blocks until queue stops being full.</span>
&lt;Queue&gt;.put_nowait(&lt;el&gt;)              <span class="hljs-comment"># Raises queue.Full exception if full.</span>
&lt;el&gt; = &lt;Queue&gt;.get()                  <span class="hljs-comment"># Blocks until queue stops being empty.</span>
&lt;el&gt; = &lt;Queue&gt;.get_nowait()           <span class="hljs-comment"># Raises queue.Empty exception if empty.</span>
</code></pre>
<div><h2 id="operator"><a href="#operator" name="operator">#</a>Operator</h2><p><strong>Module of functions that provide the functionality of operators.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> operator <span class="hljs-keyword">import</span> add, sub, mul, truediv, floordiv, mod, pow, neg, abs
<span class="hljs-keyword">from</span> operator <span class="hljs-keyword">import</span> eq, ne, lt, le, gt, ge
<span class="hljs-keyword">from</span> operator <span class="hljs-keyword">import</span> and_, or_, xor, not_
<span class="hljs-keyword">from</span> operator <span class="hljs-keyword">import</span> itemgetter, attrgetter, methodcaller
</code></pre></div>


<pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> operator <span class="hljs-keyword">as</span> op
elementwise_sum  = map(op.add, list_a, list_b)
sorted_by_second = sorted(&lt;collection&gt;, key=op.itemgetter(<span class="hljs-number">1</span>))
sorted_by_both   = sorted(&lt;collection&gt;, key=op.itemgetter(<span class="hljs-number">1</span>, <span class="hljs-number">0</span>))
product_of_elems = functools.reduce(op.mul, &lt;collection&gt;)
union_of_sets    = functools.reduce(op.or_, &lt;coll_of_sets&gt;)
LogicOp          = enum.Enum(<span class="hljs-string">'LogicOp'</span>, {<span class="hljs-string">'AND'</span>: op.and_, <span class="hljs-string">'OR'</span> : op.or_})
last_el          = op.methodcaller(<span class="hljs-string">'pop'</span>)(&lt;list&gt;)
</code></pre>
<div><h2 id="introspection"><a href="#introspection" name="introspection">#</a>Introspection</h2><p><strong>Inspecting code at runtime.</strong></p><div><h3 id="variables">Variables</h3><pre><code class="python language-python hljs">&lt;list&gt; = dir()                             <span class="hljs-comment"># Names of local variables (incl. functions).</span>
&lt;dict&gt; = vars()                            <span class="hljs-comment"># Dict of local variables. Also locals().</span>
&lt;dict&gt; = globals()                         <span class="hljs-comment"># Dict of global variables.</span>
</code></pre></div></div>



<div><h3 id="attributes-1">Attributes</h3><pre><code class="python language-python hljs">&lt;list&gt; = dir(&lt;object&gt;)                     <span class="hljs-comment"># Names of object's attributes (incl. methods).</span>
&lt;dict&gt; = vars(&lt;object&gt;)                    <span class="hljs-comment"># Dict of object's fields. Also &lt;obj&gt;.__dict__.</span>
&lt;bool&gt; = hasattr(&lt;object&gt;, <span class="hljs-string">'&lt;attr_name&gt;'</span>)  <span class="hljs-comment"># Checks if getattr() raises an error.</span>
value  = getattr(&lt;object&gt;, <span class="hljs-string">'&lt;attr_name&gt;'</span>)  <span class="hljs-comment"># Raises AttributeError if attribute is missing.</span>
setattr(&lt;object&gt;, <span class="hljs-string">'&lt;attr_name&gt;'</span>, value)    <span class="hljs-comment"># Only works on objects with __dict__ attribute.</span>
delattr(&lt;object&gt;, <span class="hljs-string">'&lt;attr_name&gt;'</span>)           <span class="hljs-comment"># Equivalent to `del &lt;object&gt;.&lt;attr_name&gt;`.</span>
</code></pre></div>

<div><h3 id="parameters-1">Parameters</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> inspect <span class="hljs-keyword">import</span> signature
&lt;sig&gt;        = signature(&lt;function&gt;)
no_of_params = len(&lt;sig&gt;.parameters)
param_names  = list(&lt;sig&gt;.parameters.keys())
param_kinds  = [a.kind <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> &lt;sig&gt;.parameters.values()]
</code></pre></div>

<div><h2 id="metaprograming"><a href="#metaprograming" name="metaprograming">#</a>Metaprograming</h2><p><strong>Code that generates code.</strong></p><div><h3 id="type-1">Type</h3><p><strong>Type is the root class. If only passed an object it returns its type (class). Otherwise it creates a new class.</strong></p><pre><code class="python language-python hljs">&lt;class&gt; = type(<span class="hljs-string">'&lt;class_name&gt;'</span>, &lt;parents_tuple&gt;, &lt;attributes_dict&gt;)</code></pre></div></div>




<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>Z = type(<span class="hljs-string">'Z'</span>, (), {<span class="hljs-string">'a'</span>: <span class="hljs-string">'abcde'</span>, <span class="hljs-string">'b'</span>: <span class="hljs-number">12345</span>})
<span class="hljs-meta">&gt;&gt;&gt; </span>z = Z()
</code></pre>
<div><h3 id="metaclass">Meta Class</h3><p><strong>A class that creates classes.</strong></p><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">my_meta_class</span><span class="hljs-params">(name, parents, attrs)</span>:</span>
    attrs[<span class="hljs-string">'a'</span>] = <span class="hljs-string">'abcde'</span>
    <span class="hljs-keyword">return</span> type(name, parents, attrs)
</code></pre></div>


<div><h4 id="or-2">Or:</h4><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyMetaClass</span><span class="hljs-params">(type)</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__new__</span><span class="hljs-params">(cls, name, parents, attrs)</span>:</span>
        attrs[<span class="hljs-string">'a'</span>] = <span class="hljs-string">'abcde'</span>
        <span class="hljs-keyword">return</span> type.__new__(cls, name, parents, attrs)
</code></pre></div>

<ul>
<li><strong>New() is a class method that gets called before init(). If it returns an instance of its class, then that instance gets passed to init() as a 'self' argument.</strong></li>
<li><strong>It receives the same arguments as init(), except for the first one that specifies the desired type of the returned instance (MyMetaClass in our case).</strong></li>
<li><strong>Like in our case, new() can also be called directly, usually from a new() method of a child class (</strong><code class="python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__new__</span><span class="hljs-params">(cls)</span>:</span> <span class="hljs-keyword">return</span> super().__new__(cls)</code><strong>).</strong></li>
<li><strong>The only difference between the examples above is that my_meta_class() returns a class of type type, while MyMetaClass() returns a class of type MyMetaClass.</strong></li>
</ul>
<div><h3 id="metaclassattribute">Metaclass Attribute</h3><p><strong>Right before a class is created it checks if it has the 'metaclass' attribute defined. If not, it recursively checks if any of his parents has it defined and eventually comes to type().</strong></p><pre><code class="python language-python hljs"><span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">MyClass</span><span class="hljs-params">(metaclass=MyMetaClass)</span>:</span>
    b = <span class="hljs-number">12345</span>
</code></pre></div>


<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>MyClass.a, MyClass.b
(<span class="hljs-string">'abcde'</span>, <span class="hljs-number">12345</span>)
</code></pre>
<div><h3 id="typediagram">Type Diagram</h3><pre><code class="python language-python hljs">type(MyClass)     == MyMetaClass     <span class="hljs-comment"># MyClass is an instance of MyMetaClass.</span>
type(MyMetaClass) == type            <span class="hljs-comment"># MyMetaClass is an instance of type.</span>
</code></pre></div>

<pre><code class="text language-text">┏━━━━━━━━━━━━━┯━━━━━━━━━━━━━┓
┃   Classes   │ Metaclasses ┃
┠─────────────┼─────────────┨
┃   MyClass ──→ MyMetaClass ┃
┃             │     ↓       ┃
┃    object ─────→ type ←╮  ┃
┃             │     ↑ ╰──╯  ┃
┃     str ──────────╯       ┃
┗━━━━━━━━━━━━━┷━━━━━━━━━━━━━┛
</code></pre>
<div><h3 id="inheritancediagram">Inheritance Diagram</h3><pre><code class="python language-python hljs">MyClass.__base__     == object       <span class="hljs-comment"># MyClass is a subclass of object.</span>
MyMetaClass.__base__ == type         <span class="hljs-comment"># MyMetaClass is a subclass of type.</span>
</code></pre></div>

<pre><code class="text language-text">┏━━━━━━━━━━━━━┯━━━━━━━━━━━━━┓
┃   Classes   │ Metaclasses ┃
┠─────────────┼─────────────┨
┃   MyClass   │ MyMetaClass ┃
┃      ↓      │     ↓       ┃
┃    object ←───── type     ┃
┃      ↑      │             ┃
┃     str     │             ┃
┗━━━━━━━━━━━━━┷━━━━━━━━━━━━━┛
</code></pre>
<div><h2 id="eval"><a href="#eval" name="eval">#</a>Eval</h2><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> ast <span class="hljs-keyword">import</span> literal_eval
<span class="hljs-meta">&gt;&gt;&gt; </span>literal_eval(<span class="hljs-string">'[1, 2, 3]'</span>)
[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>]
<span class="hljs-meta">&gt;&gt;&gt; </span>literal_eval(<span class="hljs-string">'1 + 2'</span>)
ValueError: malformed node or string
</code></pre></div>

<div><h2 id="coroutines"><a href="#coroutines" name="coroutines">#</a>Coroutines</h2><ul>
<li><strong>Coroutines have a lot in common with threads, but unlike threads, they only give up control when they call another coroutine and they don’t use as much memory.</strong></li>
<li><strong>Coroutine definition starts with <code class="python hljs"><span class="hljs-string">'async'</span></code> and its call with <code class="python hljs"><span class="hljs-string">'await'</span></code>.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'asyncio.run(&lt;coroutine&gt;)'</span></code> is the main entry point for asynchronous programs.</strong></li>
<li><strong>Functions wait(), gather() and as_completed() can be used when multiple coroutines need to be started at the same time.</strong></li>
<li><strong>Asyncio module also provides its own <a href="#queue">Queue</a>, <a href="#semaphoreeventbarrier">Event</a>, <a href="#lock">Lock</a> and <a href="#semaphore-event-barrier">Semaphore</a> classes.</strong></li>
</ul><div><h4 id="runsaterminalgamewhereyoucontrolanasteriskthatmustavoidnumbers">Runs a terminal game where you control an asterisk that must avoid numbers:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> asyncio, collections, curses, enum, random

P = collections.namedtuple(<span class="hljs-string">'P'</span>, <span class="hljs-string">'x y'</span>)         <span class="hljs-comment"># Position</span>
D = enum.Enum(<span class="hljs-string">'D'</span>, <span class="hljs-string">'n e s w'</span>)                  <span class="hljs-comment"># Direction</span>

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">(screen)</span>:</span>
    curses.curs_set(<span class="hljs-number">0</span>)                         <span class="hljs-comment"># Makes cursor invisible.</span>
    screen.nodelay(<span class="hljs-keyword">True</span>)                       <span class="hljs-comment"># Makes getch() non-blocking.</span>
    asyncio.run(main_coroutine(screen))        <span class="hljs-comment"># Starts running asyncio code.</span>

<span class="hljs-keyword">async</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main_coroutine</span><span class="hljs-params">(screen)</span>:</span>
    state = {<span class="hljs-string">'*'</span>: P(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>), **{id_: P(<span class="hljs-number">30</span>, <span class="hljs-number">10</span>) <span class="hljs-keyword">for</span> id_ <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)}}
    moves = asyncio.Queue()
    coros = (*(random_controller(id_, moves) <span class="hljs-keyword">for</span> id_ <span class="hljs-keyword">in</span> range(<span class="hljs-number">10</span>)),
             human_controller(screen, moves),
             model(moves, state, *screen.getmaxyx()),
             view(state, screen))
    <span class="hljs-keyword">await</span> asyncio.wait(coros, return_when=asyncio.FIRST_COMPLETED)

<span class="hljs-keyword">async</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">random_controller</span><span class="hljs-params">(id_, moves)</span>:</span>
    <span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
        moves.put_nowait((id_, random.choice(list(D))))
        <span class="hljs-keyword">await</span> asyncio.sleep(random.random() / <span class="hljs-number">2</span>)

<span class="hljs-keyword">async</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">human_controller</span><span class="hljs-params">(screen, moves)</span>:</span>
    <span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
        ch = screen.getch()
        key_mappings = {<span class="hljs-number">259</span>: D.n, <span class="hljs-number">261</span>: D.e, <span class="hljs-number">258</span>: D.s, <span class="hljs-number">260</span>: D.w}
        <span class="hljs-keyword">if</span> ch <span class="hljs-keyword">in</span> key_mappings:
            moves.put_nowait((<span class="hljs-string">'*'</span>, key_mappings[ch]))
        <span class="hljs-keyword">await</span> asyncio.sleep(<span class="hljs-number">0.01</span>)  

<span class="hljs-keyword">async</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">model</span><span class="hljs-params">(moves, state, height, width)</span>:</span>
    <span class="hljs-keyword">while</span> state[<span class="hljs-string">'*'</span>] <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> {p <span class="hljs-keyword">for</span> id_, p <span class="hljs-keyword">in</span> state.items() <span class="hljs-keyword">if</span> id_ != <span class="hljs-string">'*'</span>}:
        id_, d = <span class="hljs-keyword">await</span> moves.get()
        p      = state[id_]
        deltas = {D.n: P(<span class="hljs-number">0</span>, <span class="hljs-number">-1</span>), D.e: P(<span class="hljs-number">1</span>, <span class="hljs-number">0</span>), D.s: P(<span class="hljs-number">0</span>, <span class="hljs-number">1</span>), D.w: P(<span class="hljs-number">-1</span>, <span class="hljs-number">0</span>)}
        new_p  = P(p.x + deltas[d].x, p.y + deltas[d].y)
        <span class="hljs-keyword">if</span> <span class="hljs-number">0</span> &lt;= new_p.x &lt; width<span class="hljs-number">-1</span> <span class="hljs-keyword">and</span> <span class="hljs-number">0</span> &lt;= new_p.y &lt; height:
            state[id_] = new_p

<span class="hljs-keyword">async</span> <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">view</span><span class="hljs-params">(state, screen)</span>:</span>
    <span class="hljs-keyword">while</span> <span class="hljs-keyword">True</span>:
        screen.clear()
        <span class="hljs-keyword">for</span> id_, p <span class="hljs-keyword">in</span> state.items():
            screen.addstr(p.y, p.x, str(id_))
        <span class="hljs-keyword">await</span> asyncio.sleep(<span class="hljs-number">0.01</span>)  

<span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span>:
    curses.wrapper(main)
</code></pre></div></div>



<p><br></p>
<div><h1 id="libraries">Libraries</h1><div><h2 id="progressbar"><a href="#progressbar" name="progressbar">#</a>Progress Bar</h2><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install tqdm</span>
<span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> tqdm <span class="hljs-keyword">import</span> tqdm
<span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> time <span class="hljs-keyword">import</span> sleep
<span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">for</span> el <span class="hljs-keyword">in</span> tqdm([<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>], desc=<span class="hljs-string">'Processing'</span>):
<span class="hljs-meta">... </span>    sleep(<span class="hljs-number">1</span>)
Processing: 100%|████████████████████| 3/3 [00:03&lt;00:00,  1.00s/it]
</code></pre></div></div>


<div><h2 id="plot"><a href="#plot" name="plot">#</a>Plot</h2><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install matplotlib</span>
<span class="hljs-keyword">from</span> matplotlib <span class="hljs-keyword">import</span> pyplot
pyplot.plot(&lt;y_data&gt; [, label=&lt;str&gt;])
pyplot.plot(&lt;x_data&gt;, &lt;y_data&gt;)
pyplot.legend()                                <span class="hljs-comment"># Adds a legend.</span>
pyplot.savefig(&lt;path&gt;)                         <span class="hljs-comment"># Saves the figure.</span>
pyplot.show()                                  <span class="hljs-comment"># Displays the figure.</span>
pyplot.clf()                                   <span class="hljs-comment"># Clears the figure.</span>
</code></pre></div>

<div><h2 id="table"><a href="#table" name="table">#</a>Table</h2><div><h4 id="printsacsvfileasanasciitable">Prints a CSV file as an ASCII table:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install tabulate</span>
<span class="hljs-keyword">import</span> csv, tabulate
<span class="hljs-keyword">with</span> open(<span class="hljs-string">'test.csv'</span>, encoding=<span class="hljs-string">'utf-8'</span>, newline=<span class="hljs-string">''</span>) <span class="hljs-keyword">as</span> file:
    rows   = csv.reader(file)
    header = [a.title() <span class="hljs-keyword">for</span> a <span class="hljs-keyword">in</span> next(rows)]
    table  = tabulate.tabulate(rows, header)
    print(table)
</code></pre></div></div>


<div><h2 id="curses"><a href="#curses" name="curses">#</a>Curses</h2><div><h4 id="clearstheterminalprintsamessageandwaitsfortheesckeypress">Clears the terminal, prints a message and waits for the ESC key press:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> curses <span class="hljs-keyword">import</span> wrapper, curs_set, ascii
<span class="hljs-keyword">from</span> curses <span class="hljs-keyword">import</span> KEY_UP, KEY_RIGHT, KEY_DOWN, KEY_LEFT

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">()</span>:</span>
    wrapper(draw)

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">draw</span><span class="hljs-params">(screen)</span>:</span>
    curs_set(<span class="hljs-number">0</span>)                                <span class="hljs-comment"># Makes cursor invisible.</span>
    screen.nodelay(<span class="hljs-keyword">True</span>)                       <span class="hljs-comment"># Makes getch() non-blocking.</span>
    screen.clear()
    screen.addstr(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-string">'Press ESC to quit.'</span>)  <span class="hljs-comment"># Coordinates are y, x.</span>
    <span class="hljs-keyword">while</span> screen.getch() != ascii.ESC:
        <span class="hljs-keyword">pass</span>

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_border</span><span class="hljs-params">(screen)</span>:</span>
    <span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> namedtuple
    P = namedtuple(<span class="hljs-string">'P'</span>, <span class="hljs-string">'x y'</span>)
    height, width = screen.getmaxyx()
    <span class="hljs-keyword">return</span> P(width<span class="hljs-number">-1</span>, height<span class="hljs-number">-1</span>)

<span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span>:
    main()
</code></pre></div></div>


<div><h2 id="logging"><a href="#logging" name="logging">#</a>Logging</h2><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install loguru</span>
<span class="hljs-keyword">from</span> loguru <span class="hljs-keyword">import</span> logger
</code></pre></div>

<pre><code class="python language-python hljs">logger.add(<span class="hljs-string">'debug_{time}.log'</span>, colorize=<span class="hljs-keyword">True</span>)  <span class="hljs-comment"># Connects a log file.</span>
logger.add(<span class="hljs-string">'error_{time}.log'</span>, level=<span class="hljs-string">'ERROR'</span>)  <span class="hljs-comment"># Another file for errors or higher.</span>
logger.&lt;level&gt;(<span class="hljs-string">'A logging message.'</span>)
</code></pre>
<ul>
<li><strong>Levels: <code class="python hljs"><span class="hljs-string">'debug'</span></code>, <code class="python hljs"><span class="hljs-string">'info'</span></code>, <code class="python hljs"><span class="hljs-string">'success'</span></code>, <code class="python hljs"><span class="hljs-string">'warning'</span></code>, <code class="python hljs"><span class="hljs-string">'error'</span></code>, <code class="python hljs"><span class="hljs-string">'critical'</span></code>.</strong></li>
</ul>
<div><h3 id="exceptions-2">Exceptions</h3><p><strong>Exception description, stack trace and values of variables are appended automatically.</strong></p><pre><code class="python language-python hljs"><span class="hljs-keyword">try</span>:
    ...
<span class="hljs-keyword">except</span> &lt;exception&gt;:
    logger.exception(<span class="hljs-string">'An error happened.'</span>)
</code></pre></div>


<div><h3 id="rotation">Rotation</h3><p><strong>Argument that sets a condition when a new log file is created.</strong></p><pre><code class="python language-python hljs">rotation=&lt;int&gt;|&lt;datetime.timedelta&gt;|&lt;datetime.time&gt;|&lt;str&gt;
</code></pre></div>


<ul>
<li><strong><code class="python hljs"><span class="hljs-string">'&lt;int&gt;'</span></code> - Max file size in bytes.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'&lt;timedelta&gt;'</span></code> - Max age of a file.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'&lt;time&gt;'</span></code> - Time of day.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'&lt;str&gt;'</span></code> - Any of above as a string: <code class="python hljs"><span class="hljs-string">'100 MB'</span></code>, <code class="python hljs"><span class="hljs-string">'1 month'</span></code>, <code class="python hljs"><span class="hljs-string">'monday at 12:00'</span></code>, …</strong></li>
</ul>
<div><h3 id="retention">Retention</h3><p><strong>Sets a condition which old log files get deleted.</strong></p><pre><code class="python language-python hljs">retention=&lt;int&gt;|&lt;datetime.timedelta&gt;|&lt;str&gt;
</code></pre></div>


<ul>
<li><strong><code class="python hljs"><span class="hljs-string">'&lt;int&gt;'</span></code> - Max number of files.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'&lt;timedelta&gt;'</span></code> - Max age of a file.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'&lt;str&gt;'</span></code> - Max age as a string: <code class="python hljs"><span class="hljs-string">'1 week, 3 days'</span></code>, <code class="python hljs"><span class="hljs-string">'2 months'</span></code>, …</strong></li>
</ul>
<div><h2 id="scraping"><a href="#scraping" name="scraping">#</a>Scraping</h2><div><h4 id="scrapespythonsurlversionnumberandlogofromitswikipediapage">Scrapes Python's URL, version number and logo from its Wikipedia page:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install requests beautifulsoup4</span>
<span class="hljs-keyword">import</span> requests, bs4, sys
URL = <span class="hljs-string">'https://en.wikipedia.org/wiki/Python_(programming_language)'</span>
<span class="hljs-keyword">try</span>:
    html  = requests.get(URL).text
    doc   = bs4.BeautifulSoup(html, <span class="hljs-string">'html.parser'</span>)
    table = doc.find(<span class="hljs-string">'table'</span>, class_=<span class="hljs-string">'infobox vevent'</span>)
    link  = table.find(<span class="hljs-string">'th'</span>, text=<span class="hljs-string">'Website'</span>).next_sibling.a[<span class="hljs-string">'href'</span>]
    ver   = table.find(<span class="hljs-string">'th'</span>, text=<span class="hljs-string">'Stable release'</span>).next_sibling.strings.__next__()
    url_i = table.find(<span class="hljs-string">'img'</span>)[<span class="hljs-string">'src'</span>]
    image = requests.get(<span class="hljs-string">f'https:<span class="hljs-subst">{url_i}</span>'</span>).content
    <span class="hljs-keyword">with</span> open(<span class="hljs-string">'test.png'</span>, <span class="hljs-string">'wb'</span>) <span class="hljs-keyword">as</span> file:
        file.write(image)
    print(link, ver)
<span class="hljs-keyword">except</span> requests.exceptions.ConnectionError:
    print(<span class="hljs-string">"You've got problems with connection."</span>, file=sys.stderr)
</code></pre></div></div>


<div><h2 id="web"><a href="#web" name="web">#</a>Web</h2><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install bottle</span>
<span class="hljs-keyword">from</span> bottle <span class="hljs-keyword">import</span> run, route, static_file, template, post, request, response
<span class="hljs-keyword">import</span> json
</code></pre></div>

<div><h3 id="run">Run</h3><pre><code class="python language-python hljs">run(host=<span class="hljs-string">'localhost'</span>, port=<span class="hljs-number">8080</span>)        <span class="hljs-comment"># Runs locally.</span>
run(host=<span class="hljs-string">'0.0.0.0'</span>, port=<span class="hljs-number">80</span>)            <span class="hljs-comment"># Runs globally.</span>
</code></pre></div>

<div><h3 id="staticrequest">Static Request</h3><pre><code class="python language-python hljs"><span class="hljs-meta">@route('/img/&lt;image&gt;')</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">send_image</span><span class="hljs-params">(image)</span>:</span>
    <span class="hljs-keyword">return</span> static_file(image, <span class="hljs-string">'img_dir/'</span>, mimetype=<span class="hljs-string">'image/png'</span>)
</code></pre></div>

<div><h3 id="dynamicrequest">Dynamic Request</h3><pre><code class="python language-python hljs"><span class="hljs-meta">@route('/&lt;sport&gt;')</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">send_page</span><span class="hljs-params">(sport)</span>:</span>
    <span class="hljs-keyword">return</span> template(<span class="hljs-string">'&lt;h1&gt;{{title}}&lt;/h1&gt;'</span>, title=sport)
</code></pre></div>

<div><h3 id="restrequest">REST Request</h3><pre><code class="python language-python hljs"><span class="hljs-meta">@post('/odds/&lt;sport&gt;')</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">odds_handler</span><span class="hljs-params">(sport)</span>:</span>
    team = request.forms.get(<span class="hljs-string">'team'</span>)
    home_odds, away_odds = <span class="hljs-number">2.44</span>, <span class="hljs-number">3.29</span>
    response.headers[<span class="hljs-string">'Content-Type'</span>] = <span class="hljs-string">'application/json'</span>
    response.headers[<span class="hljs-string">'Cache-Control'</span>] = <span class="hljs-string">'no-cache'</span>
    <span class="hljs-keyword">return</span> json.dumps([team, home_odds, away_odds])
</code></pre></div>

<div><h4 id="test">Test:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install requests</span>
<span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">import</span> requests
<span class="hljs-meta">&gt;&gt;&gt; </span>url = <span class="hljs-string">'http://localhost:8080/odds/football'</span>
<span class="hljs-meta">&gt;&gt;&gt; </span>data = {<span class="hljs-string">'team'</span>: <span class="hljs-string">'arsenal f.c.'</span>}
<span class="hljs-meta">&gt;&gt;&gt; </span>response = requests.post(url, data=data)
<span class="hljs-meta">&gt;&gt;&gt; </span>response.json()
[<span class="hljs-string">'arsenal f.c.'</span>, <span class="hljs-number">2.44</span>, <span class="hljs-number">3.29</span>]
</code></pre></div>

<div><h2 id="profiling"><a href="#profiling" name="profiling">#</a>Profiling</h2><div><h3 id="stopwatch">Stopwatch</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> time <span class="hljs-keyword">import</span> time
start_time = time()                     <span class="hljs-comment"># Seconds since the Epoch.</span>
...
duration = time() - start_time
</code></pre></div></div>


<div><h4 id="highperformance">High performance:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> time <span class="hljs-keyword">import</span> perf_counter
start_time = perf_counter()             <span class="hljs-comment"># Seconds since restart.</span>
...
duration = perf_counter() - start_time
</code></pre></div>

<div><h3 id="timingasnippet">Timing a Snippet</h3><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span><span class="hljs-keyword">from</span> timeit <span class="hljs-keyword">import</span> timeit
<span class="hljs-meta">&gt;&gt;&gt; </span>timeit(<span class="hljs-string">'"-".join(str(i) for i in range(100))'</span>,
<span class="hljs-meta">... </span>       number=<span class="hljs-number">10000</span>, globals=globals(), setup=<span class="hljs-string">'pass'</span>)
<span class="hljs-number">0.34986</span>
</code></pre></div>

<div><h3 id="profilingbyline">Profiling by Line</h3><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install line_profiler memory_profiler</span>
<span class="hljs-meta">@profile</span>
<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">()</span>:</span>
    a = [*range(<span class="hljs-number">10000</span>)]
    b = {*range(<span class="hljs-number">10000</span>)}
main()
</code></pre></div>

<pre><code class="text language-text">$ kernprof -lv test.py
Line #   Hits     Time  Per Hit   % Time  Line Contents
=======================================================
     1                                    @profile
     2                                    def main():
     3      1   1128.0   1128.0     27.4      a = [*range(10000)]
     4      1   2994.0   2994.0     72.6      b = {*range(10000)}
</code></pre>
<pre><code class="text language-text">$ python3 -m memory_profiler test.py
Line #         Mem usage      Increment   Line Contents
=======================================================
     1        35.387 MiB     35.387 MiB   @profile
     2                                    def main():
     3        35.734 MiB      0.348 MiB       a = [*range(10000)]
     4        36.160 MiB      0.426 MiB       b = {*range(10000)}
</code></pre>
<div><h3 id="callgraph">Call Graph</h3><div><h4 id="generatesapngimageofacallgraphwithhighlightedbottlenecks">Generates a PNG image of a call graph with highlighted bottlenecks:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install pycallgraph</span>
<span class="hljs-keyword">from</span> pycallgraph <span class="hljs-keyword">import</span> output, PyCallGraph
<span class="hljs-keyword">from</span> datetime <span class="hljs-keyword">import</span> datetime
time_str = datetime.now().strftime(<span class="hljs-string">'%Y%m%d%H%M%S'</span>)
filename = <span class="hljs-string">f'profile-<span class="hljs-subst">{time_str}</span>.png'</span>
drawer = output.GraphvizOutput(output_file=filename)
<span class="hljs-keyword">with</span> PyCallGraph(drawer):
    &lt;code_to_be_profiled&gt;
</code></pre></div></div>


<div><h2 id="numpy"><a href="#numpy" name="numpy">#</a>NumPy</h2><p><strong>Array manipulation mini-language. It can run up to one hundred times faster than the equivalent Python code. An even faster alternative that runs on a GPU is called CuPy.</strong></p><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install numpy</span>
<span class="hljs-keyword">import</span> numpy <span class="hljs-keyword">as</span> np
</code></pre></div>


<pre><code class="python language-python hljs">&lt;array&gt; = np.array(&lt;list&gt;)
&lt;array&gt; = np.arange(from_inclusive, to_exclusive, ±step_size)
&lt;array&gt; = np.ones(&lt;shape&gt;)
&lt;array&gt; = np.random.randint(from_inclusive, to_exclusive, &lt;shape&gt;)
</code></pre>
<pre><code class="python language-python hljs">&lt;array&gt;.shape = &lt;shape&gt;
&lt;view&gt;  = &lt;array&gt;.reshape(&lt;shape&gt;)
&lt;view&gt;  = np.broadcast_to(&lt;array&gt;, &lt;shape&gt;)
</code></pre>
<pre><code class="python language-python hljs">&lt;array&gt; = &lt;array&gt;.sum(axis)
indexes = &lt;array&gt;.argmin(axis)
</code></pre>
<ul>
<li><strong>Shape is a tuple of dimension sizes.</strong></li>
<li><strong>Axis is the index of a dimension that gets collapsed. The leftmost dimension has index 0.</strong></li>
</ul>
<div><h3 id="indexing">Indexing</h3><pre><code class="python language-python hljs">&lt;el&gt;       = &lt;2d_array&gt;[<span class="hljs-number">0</span>, <span class="hljs-number">0</span>]        <span class="hljs-comment"># First element.</span>
&lt;1d_view&gt;  = &lt;2d_array&gt;[<span class="hljs-number">0</span>]           <span class="hljs-comment"># First row.</span>
&lt;1d_view&gt;  = &lt;2d_array&gt;[:, <span class="hljs-number">0</span>]        <span class="hljs-comment"># First column. Also [..., 0].</span>
&lt;3d_view&gt;  = &lt;2d_array&gt;[<span class="hljs-keyword">None</span>, :, :]  <span class="hljs-comment"># Expanded by dimension of size 1.</span>
</code></pre></div>

<pre><code class="python language-python hljs">&lt;1d_array&gt; = &lt;2d_array&gt;[&lt;1d_row_indexes&gt;, &lt;1d_column_indexes&gt;]
&lt;2d_array&gt; = &lt;2d_array&gt;[&lt;2d_row_indexes&gt;, &lt;2d_column_indexes&gt;]
</code></pre>
<pre><code class="python language-python hljs">&lt;2d_bools&gt; = &lt;2d_array&gt; &gt; <span class="hljs-number">0</span>
&lt;1d_array&gt; = &lt;2d_array&gt;[&lt;2d_bools&gt;]
</code></pre>
<ul>
<li><strong>If row and column indexes differ in shape, they are combined with broadcasting.</strong></li>
</ul>
<div><h3 id="broadcasting">Broadcasting</h3><p><strong>Broadcasting is a set of rules by which NumPy functions operate on arrays of different sizes and/or dimensions.</strong></p><pre><code class="python language-python hljs">left  = [[<span class="hljs-number">0.1</span>], [<span class="hljs-number">0.6</span>], [<span class="hljs-number">0.8</span>]]        <span class="hljs-comment"># Shape: (3, 1)</span>
right = [ <span class="hljs-number">0.1</span> ,  <span class="hljs-number">0.6</span> ,  <span class="hljs-number">0.8</span> ]        <span class="hljs-comment"># Shape: (3)</span>
</code></pre></div>


<div><h4 id="1ifarrayshapesdifferinlengthleftpadtheshortershapewithones">1. If array shapes differ in length, left-pad the shorter shape with ones:</h4><pre><code class="python language-python hljs">left  = [[<span class="hljs-number">0.1</span>], [<span class="hljs-number">0.6</span>], [<span class="hljs-number">0.8</span>]]        <span class="hljs-comment"># Shape: (3, 1)</span>
right = [[<span class="hljs-number">0.1</span> ,  <span class="hljs-number">0.6</span> ,  <span class="hljs-number">0.8</span>]]        <span class="hljs-comment"># Shape: (1, 3) &lt;- !</span>
</code></pre></div>

<div><h4 id="2ifanydimensionsdifferinsizeexpandtheonesthathavesize1byduplicatingtheirelements">2. If any dimensions differ in size, expand the ones that have size 1 by duplicating their elements:</h4><pre><code class="python language-python hljs">left  = [[<span class="hljs-number">0.1</span>, <span class="hljs-number">0.1</span>, <span class="hljs-number">0.1</span>], [<span class="hljs-number">0.6</span>, <span class="hljs-number">0.6</span>, <span class="hljs-number">0.6</span>], [<span class="hljs-number">0.8</span>, <span class="hljs-number">0.8</span>, <span class="hljs-number">0.8</span>]]  <span class="hljs-comment"># Shape: (3, 3) &lt;- !</span>
right = [[<span class="hljs-number">0.1</span>, <span class="hljs-number">0.6</span>, <span class="hljs-number">0.8</span>], [<span class="hljs-number">0.1</span>, <span class="hljs-number">0.6</span>, <span class="hljs-number">0.8</span>], [<span class="hljs-number">0.1</span>, <span class="hljs-number">0.6</span>, <span class="hljs-number">0.8</span>]]  <span class="hljs-comment"># Shape: (3, 3) &lt;- !</span>
</code></pre></div>

<div><h4 id="3ifneithernonmatchingdimensionhassize1raiseanerror">3. If neither non-matching dimension has size 1, raise an error.</h4><div><h3 id="example-2">Example</h3><div><h4 id="foreachpointreturnsindexofitsnearestpoint010608121">For each point returns index of its nearest point (<code class="python hljs">[<span class="hljs-number">0.1</span>, <span class="hljs-number">0.6</span>, <span class="hljs-number">0.8</span>] =&gt; [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">1</span>]</code>):</h4><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>points = np.array([<span class="hljs-number">0.1</span>, <span class="hljs-number">0.6</span>, <span class="hljs-number">0.8</span>])
 [ <span class="hljs-number">0.1</span>,  <span class="hljs-number">0.6</span>,  <span class="hljs-number">0.8</span>]
<span class="hljs-meta">&gt;&gt;&gt; </span>wrapped_points = points.reshape(<span class="hljs-number">3</span>, <span class="hljs-number">1</span>)
[[ <span class="hljs-number">0.1</span>],
 [ <span class="hljs-number">0.6</span>],
 [ <span class="hljs-number">0.8</span>]]
<span class="hljs-meta">&gt;&gt;&gt; </span>distances = wrapped_points - points
[[ <span class="hljs-number">0.</span> , <span class="hljs-number">-0.5</span>, <span class="hljs-number">-0.7</span>],
 [ <span class="hljs-number">0.5</span>,  <span class="hljs-number">0.</span> , <span class="hljs-number">-0.2</span>],
 [ <span class="hljs-number">0.7</span>,  <span class="hljs-number">0.2</span>,  <span class="hljs-number">0.</span> ]]
<span class="hljs-meta">&gt;&gt;&gt; </span>distances = np.abs(distances)
[[ <span class="hljs-number">0.</span> ,  <span class="hljs-number">0.5</span>,  <span class="hljs-number">0.7</span>],
 [ <span class="hljs-number">0.5</span>,  <span class="hljs-number">0.</span> ,  <span class="hljs-number">0.2</span>],
 [ <span class="hljs-number">0.7</span>,  <span class="hljs-number">0.2</span>,  <span class="hljs-number">0.</span> ]]
<span class="hljs-meta">&gt;&gt;&gt; </span>i = np.arange(<span class="hljs-number">3</span>)
[<span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>]
<span class="hljs-meta">&gt;&gt;&gt; </span>distances[i, i] = np.inf
[[ inf,  <span class="hljs-number">0.5</span>,  <span class="hljs-number">0.7</span>],
 [ <span class="hljs-number">0.5</span>,  inf,  <span class="hljs-number">0.2</span>],
 [ <span class="hljs-number">0.7</span>,  <span class="hljs-number">0.2</span>,  inf]]
<span class="hljs-meta">&gt;&gt;&gt; </span>distances.argmin(<span class="hljs-number">1</span>)
[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">1</span>]
</code></pre></div></div></div>



<div><h2 id="image"><a href="#image" name="image">#</a>Image</h2><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install pillow</span>
<span class="hljs-keyword">from</span> PIL <span class="hljs-keyword">import</span> Image
</code></pre></div>

<pre><code class="python language-python hljs">&lt;Image&gt; = Image.new(<span class="hljs-string">'&lt;mode&gt;'</span>, (width, height))
&lt;Image&gt; = Image.open(&lt;path&gt;)
&lt;Image&gt; = &lt;Image&gt;.convert(<span class="hljs-string">'&lt;mode&gt;'</span>)
&lt;Image&gt;.save(&lt;path&gt;)
&lt;Image&gt;.show()
</code></pre>
<pre><code class="python language-python hljs">&lt;int/tuple&gt; = &lt;Image&gt;.getpixel((x, y))          <span class="hljs-comment"># Returns a pixel.</span>
&lt;Image&gt;.putpixel((x, y), &lt;int/tuple&gt;)           <span class="hljs-comment"># Writes a pixel to the image.</span>
&lt;ImagingCore&gt; = &lt;Image&gt;.getdata()               <span class="hljs-comment"># Returns a sequence of pixels.</span>
&lt;Image&gt;.putdata(&lt;list/ImagingCore&gt;)             <span class="hljs-comment"># Writes a sequence of pixels.</span>
&lt;Image&gt;.paste(&lt;Image&gt;, (x, y))                  <span class="hljs-comment"># Writes an image to the image.</span>
</code></pre>
<pre><code class="bash language-bash hljs">&lt;2d_array&gt; = np.array(&lt;Image_L&gt;)                <span class="hljs-comment"># Creates NumPy array from greyscale image.</span>
&lt;3d_array&gt; = np.array(&lt;Image_RGB&gt;)              <span class="hljs-comment"># Creates NumPy array from color image.</span>
&lt;Image&gt;    = Image.fromarray(&lt;array&gt;)           <span class="hljs-comment"># Creates image from NumPy array of floats.</span>
</code></pre>
<div><h3 id="modes-1">Modes</h3><ul>
<li><strong><code class="python hljs"><span class="hljs-string">'1'</span></code> - 1-bit pixels, black and white, stored with one pixel per byte.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'L'</span></code> - 8-bit pixels, greyscale.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'RGB'</span></code> - 3x8-bit pixels, true color.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'RGBA'</span></code> - 4x8-bit pixels, true color with transparency mask.</strong></li>
<li><strong><code class="python hljs"><span class="hljs-string">'HSV'</span></code> - 3x8-bit pixels, Hue, Saturation, Value color space.</strong></li>
</ul><div><h3 id="examples">Examples</h3><div><h4 id="createsapngimageofarainbowgradient">Creates a PNG image of a rainbow gradient:</h4><pre><code class="python language-python hljs">WIDTH, HEIGHT = <span class="hljs-number">100</span>, <span class="hljs-number">100</span>
size = WIDTH * HEIGHT
hues = [<span class="hljs-number">255</span> * i/size <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(size)]
img = Image.new(<span class="hljs-string">'HSV'</span>, (WIDTH, HEIGHT))
img.putdata([(int(h), <span class="hljs-number">255</span>, <span class="hljs-number">255</span>) <span class="hljs-keyword">for</span> h <span class="hljs-keyword">in</span> hues])
img.convert(<span class="hljs-string">'RGB'</span>).save(<span class="hljs-string">'test.png'</span>)
</code></pre></div></div></div>




<div><h4 id="addsnoisetoapngimage">Adds noise to a PNG image:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> random <span class="hljs-keyword">import</span> randint
add_noise = <span class="hljs-keyword">lambda</span> value: max(<span class="hljs-number">0</span>, min(<span class="hljs-number">255</span>, value + randint(<span class="hljs-number">-20</span>, <span class="hljs-number">20</span>)))
img = Image.open(<span class="hljs-string">'test.png'</span>).convert(<span class="hljs-string">'HSV'</span>)
img.putdata([(add_noise(h), s, v) <span class="hljs-keyword">for</span> h, s, v <span class="hljs-keyword">in</span> img.getdata()])
img.convert(<span class="hljs-string">'RGB'</span>).save(<span class="hljs-string">'test.png'</span>)
</code></pre></div>

<div><h3 id="drawing">Drawing</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> PIL <span class="hljs-keyword">import</span> ImageDraw
</code></pre></div>

<pre><code class="python language-python hljs">&lt;ImageDraw&gt; = ImageDraw.Draw(&lt;Image&gt;)
&lt;ImageDraw&gt;.point((x, y), fill=<span class="hljs-keyword">None</span>)
&lt;ImageDraw&gt;.line((x1, y1, x2, y2 [, ...]), fill=<span class="hljs-keyword">None</span>, width=<span class="hljs-number">0</span>, joint=<span class="hljs-keyword">None</span>) 
&lt;ImageDraw&gt;.arc((x1, y1, x2, y2), from_deg, to_deg, fill=<span class="hljs-keyword">None</span>, width=<span class="hljs-number">0</span>)
&lt;ImageDraw&gt;.rectangle((x1, y1, x2, y2), fill=<span class="hljs-keyword">None</span>, outline=<span class="hljs-keyword">None</span>, width=<span class="hljs-number">0</span>)
&lt;ImageDraw&gt;.polygon((x1, y1, x2, y2 [, ...]), fill=<span class="hljs-keyword">None</span>, outline=<span class="hljs-keyword">None</span>)
&lt;ImageDraw&gt;.ellipse((x1, y1, x2, y2), fill=<span class="hljs-keyword">None</span>, outline=<span class="hljs-keyword">None</span>, width=<span class="hljs-number">0</span>)
</code></pre>
<ul>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'fill=&lt;color&gt;'</span></code> to set the primary color.</strong></li>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'outline=&lt;color&gt;'</span></code> to set the secondary color.</strong></li>
<li><strong>Color can be specified as an int, tuple, <code class="python hljs"><span class="hljs-string">'#rrggbb[aa]'</span></code> string or a color name.</strong></li>
</ul>
<div><h2 id="animation"><a href="#animation" name="animation">#</a>Animation</h2><div><h4 id="createsagifofabouncingball">Creates a GIF of a bouncing ball:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install pillow imageio</span>
<span class="hljs-keyword">from</span> PIL <span class="hljs-keyword">import</span> Image, ImageDraw
<span class="hljs-keyword">import</span> imageio
WIDTH, R = <span class="hljs-number">126</span>, <span class="hljs-number">10</span>
frames = []
<span class="hljs-keyword">for</span> velocity <span class="hljs-keyword">in</span> range(<span class="hljs-number">15</span>):
    y = sum(range(velocity+<span class="hljs-number">1</span>))
    frame = Image.new(<span class="hljs-string">'L'</span>, (WIDTH, WIDTH))
    draw  = ImageDraw.Draw(frame)
    draw.ellipse((WIDTH/<span class="hljs-number">2</span>-R, y, WIDTH/<span class="hljs-number">2</span>+R, y+R*<span class="hljs-number">2</span>), fill=<span class="hljs-string">'white'</span>)
    frames.append(frame)
frames += reversed(frames[<span class="hljs-number">1</span>:<span class="hljs-number">-1</span>])
imageio.mimsave(<span class="hljs-string">'test.gif'</span>, frames, duration=<span class="hljs-number">0.03</span>)
</code></pre></div></div>


<div><h2 id="audio"><a href="#audio" name="audio">#</a>Audio</h2><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> wave
</code></pre></div>

<pre><code class="python language-python hljs">&lt;Wave_read&gt;  = wave.open(<span class="hljs-string">'&lt;path&gt;'</span>, <span class="hljs-string">'rb'</span>)        <span class="hljs-comment"># Opens the WAV file.</span>
framerate    = &lt;Wave_read&gt;.getframerate()       <span class="hljs-comment"># Number of frames per second.</span>
nchannels    = &lt;Wave_read&gt;.getnchannels()       <span class="hljs-comment"># Number of samples per frame.</span>
sampwidth    = &lt;Wave_read&gt;.getsampwidth()       <span class="hljs-comment"># Sample size in bytes.</span>
nframes      = &lt;Wave_read&gt;.getnframes()         <span class="hljs-comment"># Number of frames.</span>
&lt;params&gt;     = &lt;Wave_read&gt;.getparams()          <span class="hljs-comment"># Immutable collection of above.</span>
&lt;bytes&gt;      = &lt;Wave_read&gt;.readframes(nframes)  <span class="hljs-comment"># Returns next 'nframes' frames.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;Wave_write&gt; = wave.open(<span class="hljs-string">'&lt;path&gt;'</span>, <span class="hljs-string">'wb'</span>)        <span class="hljs-comment"># Truncates existing file.</span>
&lt;Wave_write&gt;.setframerate(&lt;int&gt;)                <span class="hljs-comment"># 44100 for CD, 48000 for video.</span>
&lt;Wave_write&gt;.setnchannels(&lt;int&gt;)                <span class="hljs-comment"># 1 for mono, 2 for stereo.</span>
&lt;Wave_write&gt;.setsampwidth(&lt;int&gt;)                <span class="hljs-comment"># 2 for CD quality sound.</span>
&lt;Wave_write&gt;.setparams(&lt;params&gt;)                <span class="hljs-comment"># Sets all parameters.</span>
&lt;Wave_write&gt;.writeframes(&lt;bytes&gt;)               <span class="hljs-comment"># Appends frames to the file.</span>
</code></pre>
<ul>
<li><strong>Bytes object contains a sequence of frames, each consisting of one or more samples.</strong></li>
<li><strong>In a stereo signal, the first sample of a frame belongs to the left channel.</strong></li>
<li><strong>Each sample consists of one or more bytes that, when converted to an integer, indicate the displacement of a speaker membrane at a given moment.</strong></li>
<li><strong>If sample width is one, then the integer should be encoded unsigned.</strong></li>
<li><strong>For all other sizes, the integer should be encoded signed with little-endian byte order.</strong></li>
</ul>
<div><h3 id="samplevalues">Sample Values</h3><pre><code class="python hljs">┏━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━┯━━━━━━━━━━━━━┓
┃ sampwidth │     min     │ zero │     max     ┃
┠───────────┼─────────────┼──────┼─────────────┨
┃     <span class="hljs-number">1</span>     │           <span class="hljs-number">0</span> │  <span class="hljs-number">128</span> │         <span class="hljs-number">255</span> ┃
┃     <span class="hljs-number">2</span>     │      <span class="hljs-number">-32768</span> │    <span class="hljs-number">0</span> │       <span class="hljs-number">32767</span> ┃
┃     <span class="hljs-number">3</span>     │    <span class="hljs-number">-8388608</span> │    <span class="hljs-number">0</span> │     <span class="hljs-number">8388607</span> ┃
┃     <span class="hljs-number">4</span>     │ <span class="hljs-number">-2147483648</span> │    <span class="hljs-number">0</span> │  <span class="hljs-number">2147483647</span> ┃
┗━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━┷━━━━━━━━━━━━━┛
</code></pre></div>

<div><h3 id="readfloatsamplesfromwavfile">Read Float Samples from WAV File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_wav_file</span><span class="hljs-params">(filename)</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_int</span><span class="hljs-params">(bytes_obj)</span>:</span>
        an_int = int.from_bytes(bytes_obj, <span class="hljs-string">'little'</span>, signed=sampwidth!=<span class="hljs-number">1</span>)
        <span class="hljs-keyword">return</span> an_int - <span class="hljs-number">128</span> * (sampwidth == <span class="hljs-number">1</span>)
    <span class="hljs-keyword">with</span> wave.open(filename, <span class="hljs-string">'rb'</span>) <span class="hljs-keyword">as</span> file:
        sampwidth = file.getsampwidth()
        frames = file.readframes(<span class="hljs-number">-1</span>)
    bytes_samples = (frames[i: i + sampwidth] <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">0</span>, len(frames), sampwidth))
    <span class="hljs-keyword">return</span> [get_int(b) / pow(<span class="hljs-number">2</span>, sampwidth * <span class="hljs-number">8</span> - <span class="hljs-number">1</span>) <span class="hljs-keyword">for</span> b <span class="hljs-keyword">in</span> bytes_samples]
</code></pre></div>

<div><h3 id="writefloatsamplestowavfile">Write Float Samples to WAV File</h3><pre><code class="python language-python hljs"><span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">write_to_wav_file</span><span class="hljs-params">(filename, float_samples, nchannels=<span class="hljs-number">1</span>, sampwidth=<span class="hljs-number">2</span>, framerate=<span class="hljs-number">44100</span>)</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_bytes</span><span class="hljs-params">(a_float)</span>:</span>
        a_float = max(<span class="hljs-number">-1</span>, min(<span class="hljs-number">1</span> - <span class="hljs-number">2e-16</span>, a_float))
        a_float += sampwidth == <span class="hljs-number">1</span>
        a_float *= pow(<span class="hljs-number">2</span>, sampwidth * <span class="hljs-number">8</span> - <span class="hljs-number">1</span>)
        <span class="hljs-keyword">return</span> int(a_float).to_bytes(sampwidth, <span class="hljs-string">'little'</span>, signed=sampwidth!=<span class="hljs-number">1</span>) 
    <span class="hljs-keyword">with</span> wave.open(filename, <span class="hljs-string">'wb'</span>) <span class="hljs-keyword">as</span> file:
        file.setnchannels(nchannels)
        file.setsampwidth(sampwidth)
        file.setframerate(framerate)
        file.writeframes(<span class="hljs-string">b''</span>.join(get_bytes(f) <span class="hljs-keyword">for</span> f <span class="hljs-keyword">in</span> float_samples))
</code></pre></div>

<div><h3 id="examples-1">Examples</h3><div><h4 id="savesasinewavetoamonowavfile">Saves a sine wave to a mono WAV file:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> math <span class="hljs-keyword">import</span> pi, sin
samples_f = (sin(i * <span class="hljs-number">2</span> * pi * <span class="hljs-number">440</span> / <span class="hljs-number">44100</span>) <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(<span class="hljs-number">100000</span>))
write_to_wav_file(<span class="hljs-string">'test.wav'</span>, samples_f)
</code></pre></div></div>


<div><h4 id="addsnoisetoamonowavfile">Adds noise to a mono WAV file:</h4><pre><code class="python language-python hljs"><span class="hljs-keyword">from</span> random <span class="hljs-keyword">import</span> random
add_noise = <span class="hljs-keyword">lambda</span> value: value + (random() - <span class="hljs-number">0.5</span>) * <span class="hljs-number">0.03</span>
samples_f = (add_noise(f) <span class="hljs-keyword">for</span> f <span class="hljs-keyword">in</span> read_wav_file(<span class="hljs-string">'test.wav'</span>))
write_to_wav_file(<span class="hljs-string">'test.wav'</span>, samples_f)
</code></pre></div>

<div><h4 id="playsawavfile">Plays a WAV file:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install simpleaudio</span>
<span class="hljs-keyword">from</span> simpleaudio <span class="hljs-keyword">import</span> play_buffer
<span class="hljs-keyword">with</span> wave.open(<span class="hljs-string">'test.wav'</span>, <span class="hljs-string">'rb'</span>) <span class="hljs-keyword">as</span> file:
    p = file.getparams()
    frames = file.readframes(<span class="hljs-number">-1</span>)
    play_buffer(frames, p.nchannels, p.sampwidth, p.framerate)
</code></pre></div>

<div><h3 id="texttospeech">Text to Speech</h3><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install pyttsx3</span>
<span class="hljs-keyword">import</span> pyttsx3
engine = pyttsx3.init()
engine.say(<span class="hljs-string">'Sally sells seashells by the seashore.'</span>)
engine.runAndWait()
</code></pre></div>

<div><h2 id="synthesizer"><a href="#synthesizer" name="synthesizer">#</a>Synthesizer</h2><div><h4 id="playspopcornbygershonkingsley">Plays Popcorn by Gershon Kingsley:</h4><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install simpleaudio</span>
<span class="hljs-keyword">import</span> simpleaudio, math, struct
<span class="hljs-keyword">from</span> itertools <span class="hljs-keyword">import</span> chain, repeat
F  = <span class="hljs-number">44100</span>
P1 = <span class="hljs-string">'71♪,69,,71♪,66,,62♪,66,,59♪,,,'</span>
P2 = <span class="hljs-string">'71♪,73,,74♪,73,,74,,71,,73♪,71,,73,,69,,71♪,69,,71,,67,,71♪,,,'</span>
get_pause   = <span class="hljs-keyword">lambda</span> seconds: repeat(<span class="hljs-number">0</span>, int(seconds * F))
sin_f       = <span class="hljs-keyword">lambda</span> i, hz: math.sin(i * <span class="hljs-number">2</span> * math.pi * hz / F)
get_wave    = <span class="hljs-keyword">lambda</span> hz, seconds: (sin_f(i, hz) <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> range(int(seconds * F)))
get_hz      = <span class="hljs-keyword">lambda</span> key: <span class="hljs-number">8.176</span> * <span class="hljs-number">2</span> ** (int(key) / <span class="hljs-number">12</span>)
parse_note  = <span class="hljs-keyword">lambda</span> note: (get_hz(note[:<span class="hljs-number">2</span>]), <span class="hljs-number">0.25</span> <span class="hljs-keyword">if</span> <span class="hljs-string">'♪'</span> <span class="hljs-keyword">in</span> note <span class="hljs-keyword">else</span> <span class="hljs-number">0.125</span>)
get_samples = <span class="hljs-keyword">lambda</span> note: get_wave(*parse_note(note)) <span class="hljs-keyword">if</span> note <span class="hljs-keyword">else</span> get_pause(<span class="hljs-number">0.125</span>)
samples_f   = chain.from_iterable(get_samples(n) <span class="hljs-keyword">for</span> n <span class="hljs-keyword">in</span> <span class="hljs-string">f'<span class="hljs-subst">{P1}</span><span class="hljs-subst">{P1}</span><span class="hljs-subst">{P2}</span>'</span>.split(<span class="hljs-string">','</span>))
samples_b   = <span class="hljs-string">b''</span>.join(struct.pack(<span class="hljs-string">'&lt;h'</span>, int(f * <span class="hljs-number">30000</span>)) <span class="hljs-keyword">for</span> f <span class="hljs-keyword">in</span> samples_f)
simpleaudio.play_buffer(samples_b, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>, F)
</code></pre></div></div>


<div><h2 id="pygame"><a href="#pygame" name="pygame">#</a>Pygame</h2><div><h3 id="basicexample-1">Basic Example</h3><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install pygame</span>
<span class="hljs-keyword">import</span> pygame <span class="hljs-keyword">as</span> pg
pg.init()
screen = pg.display.set_mode((<span class="hljs-number">500</span>, <span class="hljs-number">500</span>))
rect = pg.Rect(<span class="hljs-number">240</span>, <span class="hljs-number">240</span>, <span class="hljs-number">20</span>, <span class="hljs-number">20</span>)
<span class="hljs-keyword">while</span> all(event.type != pg.QUIT <span class="hljs-keyword">for</span> event <span class="hljs-keyword">in</span> pg.event.get()):
    deltas = {pg.K_UP: (<span class="hljs-number">0</span>, <span class="hljs-number">-3</span>), pg.K_RIGHT: (<span class="hljs-number">3</span>, <span class="hljs-number">0</span>), pg.K_DOWN: (<span class="hljs-number">0</span>, <span class="hljs-number">3</span>), pg.K_LEFT: (<span class="hljs-number">-3</span>, <span class="hljs-number">0</span>)}
    <span class="hljs-keyword">for</span> key_code, is_pressed <span class="hljs-keyword">in</span> enumerate(pg.key.get_pressed()):
        rect = rect.move(deltas[key_code]) <span class="hljs-keyword">if</span> key_code <span class="hljs-keyword">in</span> deltas <span class="hljs-keyword">and</span> is_pressed <span class="hljs-keyword">else</span> rect
    screen.fill((<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>))
    pg.draw.rect(screen, (<span class="hljs-number">255</span>, <span class="hljs-number">255</span>, <span class="hljs-number">255</span>), rect)
    pg.display.flip()
</code></pre></div></div>


<div><h3 id="rectangle">Rectangle</h3><p><strong>Object for storing rectangular coordinates.</strong></p><pre><code class="python language-python hljs">&lt;Rect&gt; = pg.Rect(x, y, width, height)           <span class="hljs-comment"># Floats get truncated into ints.</span>
&lt;int&gt;  = &lt;Rect&gt;.x/y/centerx/centery/…           <span class="hljs-comment"># Top, right, bottom, left. Allows assignments.</span>
&lt;tup.&gt; = &lt;Rect&gt;.topleft/center/…                <span class="hljs-comment"># Topright, bottomright, bottomleft.</span>
&lt;Rect&gt; = &lt;Rect&gt;.move((x, y))                    <span class="hljs-comment"># Use move_ip() to move in place.</span>
</code></pre></div>


<pre><code class="python language-python hljs">&lt;bool&gt; = &lt;Rect&gt;.collidepoint((x, y))            <span class="hljs-comment"># Checks if rectangle contains a point.</span>
&lt;bool&gt; = &lt;Rect&gt;.colliderect(&lt;Rect&gt;)             <span class="hljs-comment"># Checks if two rectangles overlap.</span>
&lt;int&gt;  = &lt;Rect&gt;.collidelist(&lt;list_of_Rect&gt;)     <span class="hljs-comment"># Returns index of first colliding Rect or -1.</span>
&lt;list&gt; = &lt;Rect&gt;.collidelistall(&lt;list_of_Rect&gt;)  <span class="hljs-comment"># Returns indexes of all colliding Rects.</span>
</code></pre>
<div><h3 id="surface">Surface</h3><p><strong>Object for representing images.</strong></p><pre><code class="python language-python hljs">&lt;Surf&gt; = pg.display.set_mode((width, height))   <span class="hljs-comment"># Returns display surface.</span>
&lt;Surf&gt; = pg.Surface((width, height), …)         <span class="hljs-comment"># New RGB surface. Add `pg.SRCALPHA` for RGBA.</span>
&lt;Surf&gt; = pg.image.load(<span class="hljs-string">'&lt;path&gt;'</span>)                <span class="hljs-comment"># Loads the image. Format depends on source.</span>
&lt;Surf&gt; = &lt;Surf&gt;.subsurface(&lt;Rect&gt;)              <span class="hljs-comment"># Returns a subsurface.</span>
</code></pre></div>


<pre><code class="python language-python hljs">&lt;Surf&gt;.fill(color)                              <span class="hljs-comment"># Tuple, Color('#rrggbb[aa]') or Color(&lt;name&gt;).</span>
&lt;Surf&gt;.set_at((x, y), color)                    <span class="hljs-comment"># Updates pixel.</span>
&lt;Surf&gt;.blit(&lt;Surf&gt;, (x, y))                     <span class="hljs-comment"># Draws passed surface to the surface.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;Surf&gt; = pg.transform.scale(&lt;Surf&gt;, (width, height))
&lt;Surf&gt; = pg.transform.rotate(&lt;Surf&gt;, degrees)
&lt;Surf&gt; = pg.transform.flip(&lt;Surf&gt;, x_bool, y_bool)
</code></pre>
<pre><code class="python language-python hljs">pg.draw.line(&lt;Surf&gt;, color, (x1, y1), (x2, y2), width)
pg.draw.arc(&lt;Surf&gt;, color, &lt;Rect&gt;, from_radians, to_radians)
pg.draw.rect(&lt;Surf&gt;, color, &lt;Rect&gt;)
pg.draw.polygon(&lt;Surf&gt;, color, points)
pg.draw.ellipse(&lt;Surf&gt;, color, &lt;Rect&gt;)
</code></pre>
<div><h3 id="font">Font</h3><pre><code class="python language-python hljs">&lt;Font&gt; = pg.font.SysFont(<span class="hljs-string">'&lt;name&gt;'</span>, size)        <span class="hljs-comment"># Loads the system font or default if missing.</span>
&lt;Font&gt; = pg.font.Font(<span class="hljs-string">'&lt;path&gt;'</span>, size)           <span class="hljs-comment"># Loads the TTF file. Pass None for default.</span>
&lt;Surf&gt; = &lt;Font&gt;.render(text, antialias, color)  <span class="hljs-comment"># Background color can be specified at the end.</span>
</code></pre></div>

<div><h3 id="sound">Sound</h3><pre><code class="python language-python hljs">&lt;Sound&gt; = pg.mixer.Sound(<span class="hljs-string">'&lt;path&gt;'</span>)              <span class="hljs-comment"># Loads the WAV file.</span>
&lt;Sound&gt;.play()                                  <span class="hljs-comment"># Starts playing the sound.</span>
</code></pre></div>

<div><h3 id="basicmariobrothersexample">Basic Mario Brothers Example</h3><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> collections, dataclasses, enum, io, itertools <span class="hljs-keyword">as</span> it, pygame <span class="hljs-keyword">as</span> pg, urllib.request
<span class="hljs-keyword">from</span> random <span class="hljs-keyword">import</span> randint

P = collections.namedtuple(<span class="hljs-string">'P'</span>, <span class="hljs-string">'x y'</span>)          <span class="hljs-comment"># Position</span>
D = enum.Enum(<span class="hljs-string">'D'</span>, <span class="hljs-string">'n e s w'</span>)                   <span class="hljs-comment"># Direction</span>
SIZE, MAX_SPEED = <span class="hljs-number">50</span>, P(<span class="hljs-number">5</span>, <span class="hljs-number">10</span>)                  <span class="hljs-comment"># Screen size, Speed limit</span>

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">()</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_screen</span><span class="hljs-params">()</span>:</span>
        pg.init()
        <span class="hljs-keyword">return</span> pg.display.set_mode(<span class="hljs-number">2</span> * [SIZE*<span class="hljs-number">16</span>])
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_images</span><span class="hljs-params">()</span>:</span>
        url = <span class="hljs-string">'https://gto76.github.io/python-cheatsheet/web/mario_bros.png'</span>
        img = pg.image.load(io.BytesIO(urllib.request.urlopen(url).read()))
        <span class="hljs-keyword">return</span> [img.subsurface(get_rect(x, <span class="hljs-number">0</span>)) <span class="hljs-keyword">for</span> x <span class="hljs-keyword">in</span> range(img.get_width() // <span class="hljs-number">16</span>)]
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_mario</span><span class="hljs-params">()</span>:</span>
        Mario = dataclasses.make_dataclass(<span class="hljs-string">'Mario'</span>, <span class="hljs-string">'rect spd facing_left frame_cycle'</span>.split())
        <span class="hljs-keyword">return</span> Mario(get_rect(<span class="hljs-number">1</span>, <span class="hljs-number">1</span>), P(<span class="hljs-number">0</span>, <span class="hljs-number">0</span>), <span class="hljs-keyword">False</span>, it.cycle(range(<span class="hljs-number">3</span>)))
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_tiles</span><span class="hljs-params">()</span>:</span>
        positions = [p <span class="hljs-keyword">for</span> p <span class="hljs-keyword">in</span> it.product(range(SIZE), repeat=<span class="hljs-number">2</span>) <span class="hljs-keyword">if</span> {*p} &amp; {<span class="hljs-number">0</span>, SIZE<span class="hljs-number">-1</span>}] + \
            [(randint(<span class="hljs-number">1</span>, SIZE<span class="hljs-number">-2</span>), randint(<span class="hljs-number">2</span>, SIZE<span class="hljs-number">-2</span>)) <span class="hljs-keyword">for</span> _ <span class="hljs-keyword">in</span> range(SIZE**<span class="hljs-number">2</span> // <span class="hljs-number">10</span>)]
        <span class="hljs-keyword">return</span> [get_rect(*p) <span class="hljs-keyword">for</span> p <span class="hljs-keyword">in</span> positions]
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_rect</span><span class="hljs-params">(x, y)</span>:</span>
        <span class="hljs-keyword">return</span> pg.Rect(x*<span class="hljs-number">16</span>, y*<span class="hljs-number">16</span>, <span class="hljs-number">16</span>, <span class="hljs-number">16</span>)
    run(get_screen(), get_images(), get_mario(), get_tiles())

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">run</span><span class="hljs-params">(screen, images, mario, tiles)</span>:</span>
    clock = pg.time.Clock()
    <span class="hljs-keyword">while</span> all(event.type != pg.QUIT <span class="hljs-keyword">for</span> event <span class="hljs-keyword">in</span> pg.event.get()):
        keys = {pg.K_UP: D.n, pg.K_RIGHT: D.e, pg.K_DOWN: D.s, pg.K_LEFT: D.w}
        pressed = {keys.get(i) <span class="hljs-keyword">for</span> i, on <span class="hljs-keyword">in</span> enumerate(pg.key.get_pressed()) <span class="hljs-keyword">if</span> on}
        update_speed(mario, tiles, pressed)
        update_position(mario, tiles)
        draw(screen, images, mario, tiles, pressed)
        clock.tick(<span class="hljs-number">28</span>)

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">update_speed</span><span class="hljs-params">(mario, tiles, pressed)</span>:</span>
    x, y = mario.spd
    x += <span class="hljs-number">2</span> * ((D.e <span class="hljs-keyword">in</span> pressed) - (D.w <span class="hljs-keyword">in</span> pressed))
    x -= x // abs(x) <span class="hljs-keyword">if</span> x <span class="hljs-keyword">else</span> <span class="hljs-number">0</span>
    y += <span class="hljs-number">1</span> <span class="hljs-keyword">if</span> D.s <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> get_boundaries(mario.rect, tiles) <span class="hljs-keyword">else</span> (D.n <span class="hljs-keyword">in</span> pressed) * <span class="hljs-number">-10</span>
    mario.spd = P(*[max(-limit, min(limit, s)) <span class="hljs-keyword">for</span> limit, s <span class="hljs-keyword">in</span> zip(MAX_SPEED, P(x, y))])

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">update_position</span><span class="hljs-params">(mario, tiles)</span>:</span>
    p = mario.rect.topleft
    larger_speed = max(abs(s) <span class="hljs-keyword">for</span> s <span class="hljs-keyword">in</span> mario.spd)
    <span class="hljs-keyword">for</span> _ <span class="hljs-keyword">in</span> range(larger_speed):
        mario.spd = stop_on_collision(mario.spd, get_boundaries(mario.rect, tiles))
        p = P(*[a + s/larger_speed <span class="hljs-keyword">for</span> a, s <span class="hljs-keyword">in</span> zip(p, mario.spd)])
        mario.rect.topleft = p

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_boundaries</span><span class="hljs-params">(rect, tiles)</span>:</span>
    deltas = {D.n: P(<span class="hljs-number">0</span>, <span class="hljs-number">-1</span>), D.e: P(<span class="hljs-number">1</span>, <span class="hljs-number">0</span>), D.s: P(<span class="hljs-number">0</span>, <span class="hljs-number">1</span>), D.w: P(<span class="hljs-number">-1</span>, <span class="hljs-number">0</span>)}
    <span class="hljs-keyword">return</span> {d <span class="hljs-keyword">for</span> d, delta <span class="hljs-keyword">in</span> deltas.items() <span class="hljs-keyword">if</span> rect.move(delta).collidelist(tiles) != <span class="hljs-number">-1</span>}

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">stop_on_collision</span><span class="hljs-params">(spd, bounds)</span>:</span>
    <span class="hljs-keyword">return</span> P(x=<span class="hljs-number">0</span> <span class="hljs-keyword">if</span> (D.w <span class="hljs-keyword">in</span> bounds <span class="hljs-keyword">and</span> spd.x &lt; <span class="hljs-number">0</span>) <span class="hljs-keyword">or</span> (D.e <span class="hljs-keyword">in</span> bounds <span class="hljs-keyword">and</span> spd.x &gt; <span class="hljs-number">0</span>) <span class="hljs-keyword">else</span> spd.x,
             y=<span class="hljs-number">0</span> <span class="hljs-keyword">if</span> (D.n <span class="hljs-keyword">in</span> bounds <span class="hljs-keyword">and</span> spd.y &lt; <span class="hljs-number">0</span>) <span class="hljs-keyword">or</span> (D.s <span class="hljs-keyword">in</span> bounds <span class="hljs-keyword">and</span> spd.y &gt; <span class="hljs-number">0</span>) <span class="hljs-keyword">else</span> spd.y)

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">draw</span><span class="hljs-params">(screen, images, mario, tiles, pressed)</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_frame_index</span><span class="hljs-params">()</span>:</span>
        <span class="hljs-keyword">if</span> D.s <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> get_boundaries(mario.rect, tiles):
            <span class="hljs-keyword">return</span> <span class="hljs-number">4</span>
        <span class="hljs-keyword">return</span> next(mario.frame_cycle) <span class="hljs-keyword">if</span> {D.w, D.e} &amp; pressed <span class="hljs-keyword">else</span> <span class="hljs-number">6</span>
    screen.fill((<span class="hljs-number">85</span>, <span class="hljs-number">168</span>, <span class="hljs-number">255</span>))
    mario.facing_left = (D.w <span class="hljs-keyword">in</span> pressed) <span class="hljs-keyword">if</span> {D.w, D.e} &amp; pressed <span class="hljs-keyword">else</span> mario.facing_left
    screen.blit(images[get_frame_index() + mario.facing_left * <span class="hljs-number">9</span>], mario.rect)
    <span class="hljs-keyword">for</span> rect <span class="hljs-keyword">in</span> tiles:
        screen.blit(images[<span class="hljs-number">18</span> <span class="hljs-keyword">if</span> {*rect.topleft} &amp; {<span class="hljs-number">0</span>, (SIZE<span class="hljs-number">-1</span>)*<span class="hljs-number">16</span>} <span class="hljs-keyword">else</span> <span class="hljs-number">19</span>], rect)
    pg.display.flip()

<span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span>:
    main()
</code></pre></div>

<div><h2 id="pandas"><a href="#pandas" name="pandas">#</a>Pandas</h2><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install pandas</span>
<span class="hljs-keyword">import</span> pandas <span class="hljs-keyword">as</span> pd
<span class="hljs-keyword">from</span> pandas <span class="hljs-keyword">import</span> Series, DataFrame
</code></pre></div>

<div><h3 id="series">Series</h3><p><strong>Ordered dictionary with a name.</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>Series([<span class="hljs-number">1</span>, <span class="hljs-number">2</span>], index=[<span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>], name=<span class="hljs-string">'a'</span>)
x    <span class="hljs-number">1</span>
y    <span class="hljs-number">2</span>
Name: a, dtype: int64
</code></pre></div>


<pre><code class="python language-python hljs">&lt;Sr&gt; = Series(&lt;list&gt;)                         <span class="hljs-comment"># Assigns RangeIndex starting at 0.</span>
&lt;Sr&gt; = Series(&lt;dict&gt;)                         <span class="hljs-comment"># Takes dictionary's keys for index.</span>
&lt;Sr&gt; = Series(&lt;dict/Series&gt;, index=&lt;list&gt;)    <span class="hljs-comment"># Only keeps items with keys specified in index.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;el&gt; = &lt;Sr&gt;.loc[key]                          <span class="hljs-comment"># Or: &lt;Sr&gt;.iloc[index]</span>
&lt;Sr&gt; = &lt;Sr&gt;.loc[keys]                         <span class="hljs-comment"># Or: &lt;Sr&gt;.iloc[indexes]</span>
&lt;Sr&gt; = &lt;Sr&gt;.loc[from_key : to_key_inclusive]  <span class="hljs-comment"># Or: &lt;Sr&gt;.iloc[from_i : to_i_exclusive]</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;el&gt; = &lt;Sr&gt;[key/index]                        <span class="hljs-comment"># Or: &lt;Sr&gt;.key</span>
&lt;Sr&gt; = &lt;Sr&gt;[keys/indexes]                     <span class="hljs-comment"># Or: &lt;Sr&gt;[&lt;key_range/range&gt;]</span>
&lt;Sr&gt; = &lt;Sr&gt;[bools]                            <span class="hljs-comment"># Or: &lt;Sr&gt;.i/loc[bools]</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;Sr&gt; = &lt;Sr&gt; &gt;&lt;== &lt;el/Sr&gt;                      <span class="hljs-comment"># Returns a Series of bools.</span>
&lt;Sr&gt; = &lt;Sr&gt; +-*/ &lt;el/Sr&gt;                      <span class="hljs-comment"># Items with non-matching keys get value NaN.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;Sr&gt; = &lt;Sr&gt;.append(&lt;Sr&gt;)                      <span class="hljs-comment"># Or: pd.concat(&lt;coll_of_Sr&gt;)</span>
&lt;Sr&gt; = &lt;Sr&gt;.combine_first(&lt;Sr&gt;)               <span class="hljs-comment"># Adds items that are not yet present.</span>
&lt;Sr&gt;.update(&lt;Sr&gt;)                             <span class="hljs-comment"># Updates items that are already present.</span>
</code></pre>
<div><h4 id="aggregatetransformmap">Aggregate, Transform, Map:</h4><pre><code class="python language-python hljs">&lt;el&gt; = &lt;Sr&gt;.sum/max/mean/idxmax/all()         <span class="hljs-comment"># Or: &lt;Sr&gt;.aggregate(&lt;agg_func&gt;)</span>
&lt;Sr&gt; = &lt;Sr&gt;.rank/diff/cumsum/ffill/interpl()  <span class="hljs-comment"># Or: &lt;Sr&gt;.agg/transform(&lt;trans_func&gt;)</span>
&lt;Sr&gt; = &lt;Sr&gt;.fillna(&lt;el&gt;)                      <span class="hljs-comment"># Or: &lt;Sr&gt;.apply/agg/transform/map(&lt;map_func&gt;)</span>
</code></pre></div>

<ul>
<li><strong>The way <code class="python hljs"><span class="hljs-string">'aggregate()'</span></code> and <code class="python hljs"><span class="hljs-string">'transform()'</span></code> find out whether the passed function accepts an element or the whole Series is by passing it a single value at first and if it raises an error, then they pass it the whole Series.</strong></li>
</ul>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>sr = Series([<span class="hljs-number">1</span>, <span class="hljs-number">2</span>], index=[<span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>])
x    <span class="hljs-number">1</span>
y    <span class="hljs-number">2</span>
</code></pre>
<pre><code class="python hljs">┏━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
┃             │    <span class="hljs-string">'sum'</span>    │   [<span class="hljs-string">'sum'</span>]   │ {<span class="hljs-string">'s'</span>: <span class="hljs-string">'sum'</span>}  ┃
┠─────────────┼─────────────┼─────────────┼───────────────┨
┃ sr.apply(…) │      <span class="hljs-number">3</span>      │    sum  <span class="hljs-number">3</span>   │     s  <span class="hljs-number">3</span>      ┃
┃ sr.agg(…)   │             │             │               ┃
┗━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
</code></pre>
<pre><code class="python hljs">┏━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
┃             │    <span class="hljs-string">'rank'</span>   │   [<span class="hljs-string">'rank'</span>]  │ {<span class="hljs-string">'r'</span>: <span class="hljs-string">'rank'</span>} ┃
┠─────────────┼─────────────┼─────────────┼───────────────┨
┃ sr.apply(…) │             │      rank   │               ┃
┃ sr.agg(…)   │     x  <span class="hljs-number">1</span>    │   x     <span class="hljs-number">1</span>   │    r  x  <span class="hljs-number">1</span>    ┃
┃ sr.trans(…) │     y  <span class="hljs-number">2</span>    │   y     <span class="hljs-number">2</span>   │       y  <span class="hljs-number">2</span>    ┃
┗━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
</code></pre>
<ul>
<li><strong>Last result has a hierarchical index. Use <code class="python hljs"><span class="hljs-string">'&lt;Sr&gt;[key_1, key_2]'</span></code> to get its values.</strong></li>
</ul>
<div><h3 id="dataframe">DataFrame</h3><p><strong>Table with labeled rows and columns.</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>DataFrame([[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>], [<span class="hljs-number">3</span>, <span class="hljs-number">4</span>]], index=[<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>], columns=[<span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>])
   x  y
a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span>
b  <span class="hljs-number">3</span>  <span class="hljs-number">4</span>
</code></pre></div>


<pre><code class="python language-python hljs">&lt;DF&gt;    = DataFrame(&lt;list_of_rows&gt;)           <span class="hljs-comment"># Rows can be either lists, dicts or series.</span>
&lt;DF&gt;    = DataFrame(&lt;dict_of_columns&gt;)        <span class="hljs-comment"># Columns can be either lists, dicts or series.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;el&gt;    = &lt;DF&gt;.loc[row_key, column_key]       <span class="hljs-comment"># Or: &lt;DF&gt;.iloc[row_index, column_index]</span>
&lt;Sr/DF&gt; = &lt;DF&gt;.loc[row_key/s]                 <span class="hljs-comment"># Or: &lt;DF&gt;.iloc[row_index/es]</span>
&lt;Sr/DF&gt; = &lt;DF&gt;.loc[:, column_key/s]           <span class="hljs-comment"># Or: &lt;DF&gt;.iloc[:, column_index/es]</span>
&lt;DF&gt;    = &lt;DF&gt;.loc[row_bools, column_bools]   <span class="hljs-comment"># Or: &lt;DF&gt;.iloc[row_bools, column_bools]</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;Sr/DF&gt; = &lt;DF&gt;[column_key/s]                  <span class="hljs-comment"># Or: &lt;DF&gt;.column_key</span>
&lt;DF&gt;    = &lt;DF&gt;[row_bools]                     <span class="hljs-comment"># Keeps rows as specified by bools.</span>
&lt;DF&gt;    = &lt;DF&gt;[&lt;DF_of_bools&gt;]                 <span class="hljs-comment"># Assigns NaN to False values.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;DF&gt;    = &lt;DF&gt; &gt;&lt;== &lt;el/Sr/DF&gt;                <span class="hljs-comment"># Returns DataFrame of bools.</span>
&lt;DF&gt;    = &lt;DF&gt; +-*/ &lt;el/Sr/DF&gt;                <span class="hljs-comment"># Items with non-matching keys get value NaN.</span>
</code></pre>
<pre><code class="python language-python hljs">&lt;DF&gt;    = &lt;DF&gt;.set_index(column_key)          <span class="hljs-comment"># Replaces row keys with values from a column.</span>
&lt;DF&gt;    = &lt;DF&gt;.reset_index()                  <span class="hljs-comment"># Moves row keys to column named index.</span>
&lt;DF&gt;    = &lt;DF&gt;.filter(<span class="hljs-string">'&lt;regex&gt;'</span>, axis=<span class="hljs-number">1</span>)      <span class="hljs-comment"># Only keeps columns whose key matches the regex.</span>
&lt;DF&gt;    = &lt;DF&gt;.melt(id_vars=column_key/s)     <span class="hljs-comment"># Converts DF from wide to long format.</span>
</code></pre>
<div><h4 id="mergejoinconcat">Merge, Join, Concat:</h4><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>l = DataFrame([[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>], [<span class="hljs-number">3</span>, <span class="hljs-number">4</span>]], index=[<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>], columns=[<span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>])
   x  y 
a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span> 
b  <span class="hljs-number">3</span>  <span class="hljs-number">4</span> 
<span class="hljs-meta">&gt;&gt;&gt; </span>r = DataFrame([[<span class="hljs-number">4</span>, <span class="hljs-number">5</span>], [<span class="hljs-number">6</span>, <span class="hljs-number">7</span>]], index=[<span class="hljs-string">'b'</span>, <span class="hljs-string">'c'</span>], columns=[<span class="hljs-string">'y'</span>, <span class="hljs-string">'z'</span>])
   y  z
b  <span class="hljs-number">4</span>  <span class="hljs-number">5</span>
c  <span class="hljs-number">6</span>  <span class="hljs-number">7</span>
</code></pre></div>

<pre><code class="python hljs">┏━━━━━━━━━━━━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━┯━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃                        │    <span class="hljs-string">'outer'</span>    │   <span class="hljs-string">'inner'</span>  │   <span class="hljs-string">'left'</span>   │       Description        ┃
┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
┃ l.merge(r, on=<span class="hljs-string">'y'</span>,     │    x   y   z  │ x   y   z  │ x   y   z  │ Joins/merges on column.  ┃
┃            how=…)      │ <span class="hljs-number">0</span>  <span class="hljs-number">1</span>   <span class="hljs-number">2</span>   .  │ <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │ <span class="hljs-number">1</span>   <span class="hljs-number">2</span>   .  │ Also accepts left_on and ┃
┃                        │ <span class="hljs-number">1</span>  <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │            │ <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │ right_on parameters.     ┃
┃                        │ <span class="hljs-number">2</span>  .   <span class="hljs-number">6</span>   <span class="hljs-number">7</span>  │            │            │ Uses <span class="hljs-string">'inner'</span> by default. ┃
┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
┃ l.join(r, lsuffix=<span class="hljs-string">'l'</span>, │    x yl yr  z │            │ x yl yr  z │ Joins/merges on row keys.┃
┃           rsuffix=<span class="hljs-string">'r'</span>, │ a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span>  .  . │ x yl yr  z │ <span class="hljs-number">1</span>  <span class="hljs-number">2</span>  .  . │ Uses <span class="hljs-string">'left'</span> by default.  ┃
┃           how=…)       │ b  <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ If r is a series, it is  ┃
┃                        │ c  .  .  <span class="hljs-number">6</span>  <span class="hljs-number">7</span> │            │            │ first converted to DF.   ┃
┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
┃ pd.concat([l, r],      │    x   y   z  │     y      │            │ Adds rows at the bottom. ┃
┃           axis=<span class="hljs-number">0</span>,      │ a  <span class="hljs-number">1</span>   <span class="hljs-number">2</span>   .  │     <span class="hljs-number">2</span>      │            │ Uses <span class="hljs-string">'outer'</span> by default. ┃
┃           join=…)      │ b  <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   .  │     <span class="hljs-number">4</span>      │            │ By default works the     ┃
┃                        │ b  .   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │     <span class="hljs-number">4</span>      │            │ same as `l.append(r)`.   ┃
┃                        │ c  .   <span class="hljs-number">6</span>   <span class="hljs-number">7</span>  │     <span class="hljs-number">6</span>      │            │                          ┃
┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
┃ pd.concat([l, r],      │    x  y  y  z │            │            │ Adds columns at the      ┃
┃           axis=<span class="hljs-number">1</span>,      │ a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span>  .  . │ x  y  y  z │            │ right end.               ┃
┃           join=…)      │ b  <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │ <span class="hljs-number">3</span>  <span class="hljs-number">4</span>  <span class="hljs-number">4</span>  <span class="hljs-number">5</span> │            │ Uses <span class="hljs-string">'outer'</span> by default. ┃
┃                        │ c  .  .  <span class="hljs-number">6</span>  <span class="hljs-number">7</span> │            │            │                          ┃
┠────────────────────────┼───────────────┼────────────┼────────────┼──────────────────────────┨
┃ l.combine_first(r)     │    x   y   z  │            │            │ Adds missing rows and    ┃
┃                        │ a  <span class="hljs-number">1</span>   <span class="hljs-number">2</span>   .  │            │            │ columns.                 ┃
┃                        │ b  <span class="hljs-number">3</span>   <span class="hljs-number">4</span>   <span class="hljs-number">5</span>  │            │            │                          ┃
┃                        │ c  .   <span class="hljs-number">6</span>   <span class="hljs-number">7</span>  │            │            │                          ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━┷━━━━━━━━━━━━━━━━━━━━━━━━━━┛
</code></pre>
<div><h4 id="aggregatetransformmap-1">Aggregate, Transform, Map:</h4><pre><code class="python language-python hljs">&lt;Sr&gt; = &lt;DF&gt;.sum/max/mean/idxmax/all()         <span class="hljs-comment"># Or: &lt;DF&gt;.apply/agg/transform(&lt;agg_func&gt;)</span>
&lt;DF&gt; = &lt;DF&gt;.rank/diff/cumsum/ffill/interpl()  <span class="hljs-comment"># Or: &lt;DF&gt;.apply/agg/transform(&lt;trans_func&gt;)</span>
&lt;DF&gt; = &lt;DF&gt;.fillna(&lt;el&gt;)                      <span class="hljs-comment"># Or: &lt;DF&gt;.applymap(&lt;map_func&gt;)</span>
</code></pre></div>

<ul>
<li><strong>All operations operate on columns by default. Use <code class="python hljs"><span class="hljs-string">'axis=1'</span></code> parameter to process the rows instead.</strong> </li>
</ul>
<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>df = DataFrame([[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>], [<span class="hljs-number">3</span>, <span class="hljs-number">4</span>]], index=[<span class="hljs-string">'a'</span>, <span class="hljs-string">'b'</span>], columns=[<span class="hljs-string">'x'</span>, <span class="hljs-string">'y'</span>])
   x  y
a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span>
b  <span class="hljs-number">3</span>  <span class="hljs-number">4</span>
</code></pre>
<pre><code class="python hljs">┏━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
┃             │    <span class="hljs-string">'sum'</span>    │   [<span class="hljs-string">'sum'</span>]   │ {<span class="hljs-string">'x'</span>: <span class="hljs-string">'sum'</span>}  ┃
┠─────────────┼─────────────┼─────────────┼───────────────┨
┃ df.apply(…) │             │       x  y  │               ┃
┃ df.agg(…)   │     x  <span class="hljs-number">4</span>    │  sum  <span class="hljs-number">4</span>  <span class="hljs-number">6</span>  │     x  <span class="hljs-number">4</span>      ┃
┃             │     y  <span class="hljs-number">6</span>    │             │               ┃
┗━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
</code></pre>
<pre><code class="python hljs">┏━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
┃             │    <span class="hljs-string">'rank'</span>   │   [<span class="hljs-string">'rank'</span>]  │ {<span class="hljs-string">'x'</span>: <span class="hljs-string">'rank'</span>} ┃
┠─────────────┼─────────────┼─────────────┼───────────────┨
┃ df.apply(…) │      x  y   │      x    y │        x      ┃
┃ df.agg(…)   │   a  <span class="hljs-number">1</span>  <span class="hljs-number">1</span>   │   rank rank │     a  <span class="hljs-number">1</span>      ┃
┃ df.trans(…) │   b  <span class="hljs-number">2</span>  <span class="hljs-number">2</span>   │ a    <span class="hljs-number">1</span>    <span class="hljs-number">1</span> │     b  <span class="hljs-number">2</span>      ┃
┃             │             │ b    <span class="hljs-number">2</span>    <span class="hljs-number">2</span> │               ┃
┗━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
</code></pre>
<ul>
<li><strong>Use <code class="python hljs"><span class="hljs-string">'&lt;DF&gt;[col_key_1, col_key_2][row_key]'</span></code> to get the fifth result's values.</strong></li>
</ul>
<div><h4 id="encodedecode">Encode, Decode:</h4><pre><code class="python language-python hljs">&lt;DF&gt; = pd.read_json/html(<span class="hljs-string">'&lt;str/path/url&gt;'</span>)
&lt;DF&gt; = pd.read_csv/pickle/excel(<span class="hljs-string">'&lt;path/url&gt;'</span>)
&lt;DF&gt; = pd.read_sql(<span class="hljs-string">'&lt;table_name/query&gt;'</span>, &lt;connection&gt;)
&lt;DF&gt; = pd.read_clipboard()
</code></pre></div>

<pre><code class="python language-python hljs">&lt;dict&gt; = &lt;DF&gt;.to_dict([<span class="hljs-string">'d/l/s/sp/r/i'</span>])
&lt;str&gt;  = &lt;DF&gt;.to_json/html/csv/markdown/latex([&lt;path&gt;])
&lt;DF&gt;.to_pickle/excel(&lt;path&gt;)
&lt;DF&gt;.to_sql(<span class="hljs-string">'&lt;table_name&gt;'</span>, &lt;connection&gt;)
</code></pre>
<div><h3 id="groupby">GroupBy</h3><p><strong>Object that groups together rows of a dataframe based on the value of the passed column.</strong></p><pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>df = DataFrame([[<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>], [<span class="hljs-number">4</span>, <span class="hljs-number">5</span>, <span class="hljs-number">6</span>], [<span class="hljs-number">7</span>, <span class="hljs-number">8</span>, <span class="hljs-number">6</span>]], index=list(<span class="hljs-string">'abc'</span>), columns=list(<span class="hljs-string">'xyz'</span>))
<span class="hljs-meta">&gt;&gt;&gt; </span>df.groupby(<span class="hljs-string">'z'</span>).get_group(<span class="hljs-number">3</span>)
   x  y
a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span>
<span class="hljs-meta">&gt;&gt;&gt; </span>df.groupby(<span class="hljs-string">'z'</span>).get_group(<span class="hljs-number">6</span>)
   x  y
b  <span class="hljs-number">4</span>  <span class="hljs-number">5</span>
c  <span class="hljs-number">7</span>  <span class="hljs-number">8</span>
</code></pre></div>


<pre><code class="python language-python hljs">&lt;GB&gt; = &lt;DF&gt;.groupby(column_key/s)             <span class="hljs-comment"># DF is split into groups based on passed column.</span>
&lt;DF&gt; = &lt;GB&gt;.get_group(group_key/s)            <span class="hljs-comment"># Selects a group by value of grouping column.</span>
</code></pre>
<div><h4 id="aggregatetransformmap-2">Aggregate, Transform, Map:</h4><pre><code class="python language-python hljs">&lt;DF&gt; = &lt;GB&gt;.sum/max/mean/idxmax/all()         <span class="hljs-comment"># Or: &lt;GB&gt;.apply/agg(&lt;agg_func&gt;)</span>
&lt;DF&gt; = &lt;GB&gt;.rank/diff/cumsum/ffill()          <span class="hljs-comment"># Or: &lt;GB&gt;.aggregate(&lt;trans_func&gt;)  </span>
&lt;DF&gt; = &lt;GB&gt;.fillna(&lt;el&gt;)                      <span class="hljs-comment"># Or: &lt;GB&gt;.transform(&lt;map_func&gt;)</span>
</code></pre></div>

<pre><code class="python language-python hljs"><span class="hljs-meta">&gt;&gt;&gt; </span>gb = df.groupby(<span class="hljs-string">'z'</span>)
      x  y  z
<span class="hljs-number">3</span>: a  <span class="hljs-number">1</span>  <span class="hljs-number">2</span>  <span class="hljs-number">3</span>
<span class="hljs-number">6</span>: b  <span class="hljs-number">4</span>  <span class="hljs-number">5</span>  <span class="hljs-number">6</span>
   c  <span class="hljs-number">7</span>  <span class="hljs-number">8</span>  <span class="hljs-number">6</span>
</code></pre>
<pre><code class="python hljs">┏━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━┯━━━━━━━━━━━━━━━┓
┃             │    <span class="hljs-string">'sum'</span>    │    <span class="hljs-string">'rank'</span>   │   [<span class="hljs-string">'rank'</span>]  │ {<span class="hljs-string">'x'</span>: <span class="hljs-string">'rank'</span>} ┃
┠─────────────┼─────────────┼─────────────┼─────────────┼───────────────┨
┃ gb.agg(…)   │      x   y  │      x  y   │      x    y │        x      ┃
┃             │  z          │   a  <span class="hljs-number">1</span>  <span class="hljs-number">1</span>   │   rank rank │     a  <span class="hljs-number">1</span>      ┃
┃             │  <span class="hljs-number">3</span>   <span class="hljs-number">1</span>   <span class="hljs-number">2</span>  │   b  <span class="hljs-number">1</span>  <span class="hljs-number">1</span>   │ a    <span class="hljs-number">1</span>    <span class="hljs-number">1</span> │     b  <span class="hljs-number">1</span>      ┃
┃             │  <span class="hljs-number">6</span>  <span class="hljs-number">11</span>  <span class="hljs-number">13</span>  │   c  <span class="hljs-number">2</span>  <span class="hljs-number">2</span>   │ b    <span class="hljs-number">1</span>    <span class="hljs-number">1</span> │     c  <span class="hljs-number">2</span>      ┃
┃             │             │             │ c    <span class="hljs-number">2</span>    <span class="hljs-number">2</span> │               ┃
┠─────────────┼─────────────┼─────────────┼─────────────┼───────────────┨
┃ gb.trans(…) │      x   y  │      x  y   │             │               ┃
┃             │  a   <span class="hljs-number">1</span>   <span class="hljs-number">2</span>  │   a  <span class="hljs-number">1</span>  <span class="hljs-number">1</span>   │             │               ┃
┃             │  b  <span class="hljs-number">11</span>  <span class="hljs-number">13</span>  │   b  <span class="hljs-number">1</span>  <span class="hljs-number">1</span>   │             │               ┃
┃             │  c  <span class="hljs-number">11</span>  <span class="hljs-number">13</span>  │   c  <span class="hljs-number">1</span>  <span class="hljs-number">1</span>   │             │               ┃
┗━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━┷━━━━━━━━━━━━━━━┛
</code></pre>
<div><h3 id="rolling">Rolling</h3><p><strong>Object for rolling window calculations.</strong></p><pre><code class="python language-python hljs">&lt;R_Sr/R_DF/R_GB&gt; = &lt;Sr/DF/GB&gt;.rolling(window_size)  <span class="hljs-comment"># Also: `min_periods=None, center=False`.</span>
&lt;R_Sr/R_DF&gt;      = &lt;R_DF/R_GB&gt;[column_key/s]        <span class="hljs-comment"># Or: &lt;R&gt;.column_key</span>
&lt;Sr/DF/DF&gt;       = &lt;R_Sr/R_DF/R_GB&gt;.sum/max/mean()  <span class="hljs-comment"># Or: &lt;R&gt;.apply/agg(&lt;agg_func/str&gt;)</span>
</code></pre></div>


<div><h2 id="plotly"><a href="#plotly" name="plotly">#</a>Plotly</h2><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install plotly kaleido</span>
<span class="hljs-keyword">from</span> plotly.express <span class="hljs-keyword">import</span> line
&lt;Figure&gt; = line(&lt;DF&gt;, x=&lt;col_name&gt;, y=&lt;col_name&gt;)        <span class="hljs-comment"># Or: line(x=&lt;list&gt;, y=&lt;list&gt;)</span>
&lt;Figure&gt;.update_layout(margin=dict(t=<span class="hljs-number">0</span>, r=<span class="hljs-number">0</span>, b=<span class="hljs-number">0</span>, l=<span class="hljs-number">0</span>))  <span class="hljs-comment"># Or: paper_bgcolor='rgba(0, 0, 0, 0)'</span>
&lt;Figure&gt;.write_html/json/image(<span class="hljs-string">'&lt;path&gt;'</span>)                 <span class="hljs-comment"># Also: &lt;Figure&gt;.show()</span>
</code></pre></div>

<div><h4 id="coviddeathsbycontinent">Covid deaths by continent:</h4><p></p><div id="2a950764-39fc-416d-97fe-0a6226a3095f" class="plotly-graph-div" style="height:340px; width:100%;"></div><pre><code class="python language-python hljs">covid = pd.read_csv(<span class="hljs-string">'https://covid.ourworldindata.org/data/owid-covid-data.csv'</span>, 
                    usecols=[<span class="hljs-string">'iso_code'</span>, <span class="hljs-string">'date'</span>, <span class="hljs-string">'total_deaths'</span>, <span class="hljs-string">'population'</span>])
continents = pd.read_csv(<span class="hljs-string">'https://datahub.io/JohnSnowLabs/country-and-continent-codes-'</span> + \
                         <span class="hljs-string">'list/r/country-and-continent-codes-list-csv.csv'</span>,
                         usecols=[<span class="hljs-string">'Three_Letter_Country_Code'</span>, <span class="hljs-string">'Continent_Name'</span>])
df = pd.merge(covid, continents, left_on=<span class="hljs-string">'iso_code'</span>, right_on=<span class="hljs-string">'Three_Letter_Country_Code'</span>)
df = df.groupby([<span class="hljs-string">'Continent_Name'</span>, <span class="hljs-string">'date'</span>]).sum().reset_index()
df[<span class="hljs-string">'Total Deaths per Million'</span>] = df.total_deaths * <span class="hljs-number">1e6</span> / df.population
df = df[(<span class="hljs-string">'2020-03-14'</span> &lt; df.date) &amp; (df.date &lt; <span class="hljs-string">'2020-11-25'</span>)]
df = df.rename({<span class="hljs-string">'date'</span>: <span class="hljs-string">'Date'</span>, <span class="hljs-string">'Continent_Name'</span>: <span class="hljs-string">'Continent'</span>}, axis=<span class="hljs-string">'columns'</span>)
line(df, x=<span class="hljs-string">'Date'</span>, y=<span class="hljs-string">'Total Deaths per Million'</span>, color=<span class="hljs-string">'Continent'</span>).show()
</code></pre></div>



<div><h4 id="confirmedcovidcasesdowjonesgoldandbitcoinprice">Confirmed covid cases, Dow Jones, gold, and Bitcoin price:</h4><p></p><div id="e23ccacc-a456-478b-b467-7282a2165921" class="plotly-graph-div" style="height:315px; width:100%;"></div><pre><code class="python language-python hljs"><span class="hljs-keyword">import</span> pandas <span class="hljs-keyword">as</span> pd
<span class="hljs-keyword">import</span> plotly.graph_objects <span class="hljs-keyword">as</span> go
<span class="hljs-keyword">import</span> datetime

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">()</span>:</span>
    display_data(wrangle_data(*scrape_data()))

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">scrape_data</span><span class="hljs-params">()</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">scrape_yahoo</span><span class="hljs-params">(id_)</span>:</span>
        BASE_URL = <span class="hljs-string">'https://query1.finance.yahoo.com/v7/finance/download/'</span>
        now = int(datetime.datetime.now().timestamp())
        url = <span class="hljs-string">f'<span class="hljs-subst">{BASE_URL}</span><span class="hljs-subst">{id_}</span>?period1=1579651200&amp;period2=<span class="hljs-subst">{now}</span>&amp;interval=1d&amp;events=history'</span>
        <span class="hljs-keyword">return</span> pd.read_csv(url, usecols=[<span class="hljs-string">'Date'</span>, <span class="hljs-string">'Close'</span>]).set_index(<span class="hljs-string">'Date'</span>).Close
    covid = pd.read_csv(<span class="hljs-string">'https://covid.ourworldindata.org/data/owid-covid-data.csv'</span>,
                        usecols=[<span class="hljs-string">'location'</span>, <span class="hljs-string">'date'</span>, <span class="hljs-string">'total_cases'</span>])
    covid = covid[covid.location == <span class="hljs-string">'World'</span>].set_index(<span class="hljs-string">'date'</span>).total_cases
    dow, gold, bitcoin = [scrape_yahoo(id_) <span class="hljs-keyword">for</span> id_ <span class="hljs-keyword">in</span> (<span class="hljs-string">'^DJI'</span>, <span class="hljs-string">'GC=F'</span>, <span class="hljs-string">'BTC-USD'</span>)]
    dow.name, gold.name, bitcoin.name = <span class="hljs-string">'Dow Jones'</span>, <span class="hljs-string">'Gold'</span>, <span class="hljs-string">'Bitcoin'</span>
    <span class="hljs-keyword">return</span> covid, dow, gold, bitcoin

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">wrangle_data</span><span class="hljs-params">(covid, dow, gold, bitcoin)</span>:</span>
    df = pd.concat([dow, gold, bitcoin], axis=<span class="hljs-number">1</span>)
    df = df.sort_index().interpolate()
    df = df.rolling(<span class="hljs-number">10</span>, min_periods=<span class="hljs-number">1</span>, center=<span class="hljs-keyword">True</span>).mean()
    df = df.loc[<span class="hljs-string">'2020-02-23'</span>:].iloc[:<span class="hljs-number">-2</span>]
    df = (df / df.iloc[<span class="hljs-number">0</span>]) * <span class="hljs-number">100</span>
    <span class="hljs-keyword">return</span> pd.concat([covid, df], axis=<span class="hljs-number">1</span>, join=<span class="hljs-string">'inner'</span>)

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">display_data</span><span class="hljs-params">(df)</span>:</span>
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">get_trace</span><span class="hljs-params">(col_name)</span>:</span>
        <span class="hljs-keyword">return</span> go.Scatter(x=df.index, y=df[col_name], name=col_name, yaxis=<span class="hljs-string">'y2'</span>)
    traces = [get_trace(col_name) <span class="hljs-keyword">for</span> col_name <span class="hljs-keyword">in</span> df.columns[<span class="hljs-number">1</span>:]]
    traces.append(go.Scatter(x=df.index, y=df.total_cases, name=<span class="hljs-string">'Total Cases'</span>, yaxis=<span class="hljs-string">'y1'</span>))
    figure = go.Figure()
    figure.add_traces(traces)
    figure.update_layout(
        yaxis1=dict(title=<span class="hljs-string">'Total Cases'</span>, rangemode=<span class="hljs-string">'tozero'</span>),
        yaxis2=dict(title=<span class="hljs-string">'%'</span>, rangemode=<span class="hljs-string">'tozero'</span>, overlaying=<span class="hljs-string">'y'</span>, side=<span class="hljs-string">'right'</span>),
        legend=dict(x=<span class="hljs-number">1.1</span>)
    ).show()

<span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span>:
    main()
</code></pre></div>



<div><h2 id="pysimplegui"><a href="#pysimplegui" name="pysimplegui">#</a>PySimpleGUI</h2><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install PySimpleGUI</span>
<span class="hljs-keyword">import</span> PySimpleGUI <span class="hljs-keyword">as</span> sg
layout = [[sg.Text(<span class="hljs-string">"What's your name?"</span>)], [sg.Input()], [sg.Button(<span class="hljs-string">'Ok'</span>)]]
window = sg.Window(<span class="hljs-string">'Window Title'</span>, layout)
event, values = window.read()
print(<span class="hljs-string">f'Hello <span class="hljs-subst">{values[<span class="hljs-number">0</span>]}</span>!'</span> <span class="hljs-keyword">if</span> event == <span class="hljs-string">'Ok'</span> <span class="hljs-keyword">else</span> <span class="hljs-string">''</span>)
</code></pre></div>

<div><h2 id="appendix"><a href="#appendix" name="appendix">#</a>Appendix</h2><div><h3 id="cython">Cython</h3><p><strong>Library that compiles Python code into C.</strong></p><pre><code class="python language-python hljs"><span class="hljs-comment"># $ pip3 install cython</span>
<span class="hljs-keyword">import</span> pyximport; pyximport.install()
<span class="hljs-keyword">import</span> &lt;cython_script&gt;
&lt;cython_script&gt;.main()
</code></pre></div></div>



<div><h4 id="definitions">Definitions:</h4><ul>
<li><strong>All <code class="python hljs"><span class="hljs-string">'cdef'</span></code> definitions are optional, but they contribute to the speed-up.</strong></li>
<li><strong>Script needs to be saved with a <code class="python hljs"><span class="hljs-string">'pyx'</span></code> extension.</strong></li>
</ul><pre><code class="python language-python hljs">cdef &lt;type&gt; &lt;var_name&gt; = &lt;el&gt;
cdef &lt;type&gt;[n_elements] &lt;var_name&gt; = [&lt;el_1&gt;, &lt;el_2&gt;, ...]
cdef &lt;type/void&gt; &lt;func_name&gt;(&lt;type&gt; &lt;arg_name_1&gt;, ...):
</code></pre></div>


<pre><code class="python language-python hljs">cdef <span class="hljs-class"><span class="hljs-keyword">class</span> &lt;<span class="hljs-title">class_name</span>&gt;:</span>
    cdef public &lt;type&gt; &lt;attr_name&gt;
    <span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">__init__</span><span class="hljs-params">(self, &lt;type&gt; &lt;arg_name&gt;)</span>:</span>
        self.&lt;attr_name&gt; = &lt;arg_name&gt;
</code></pre>
<pre><code class="python language-python hljs">cdef enum &lt;enum_name&gt;: &lt;member_name_1&gt;, &lt;member_name_2&gt;, ...
</code></pre>
<div><h3 id="pyinstaller">PyInstaller</h3><pre><code class="bash language-bash hljs">$ pip3 install pyinstaller
$ pyinstaller script.py                        <span class="hljs-comment"># Compiles into './dist/script' directory.</span>
$ pyinstaller script.py --onefile              <span class="hljs-comment"># Compiles into './dist/script' console app.</span>
$ pyinstaller script.py --windowed             <span class="hljs-comment"># Compiles into './dist/script' windowed app.</span>
$ pyinstaller script.py --add-data '&lt;path&gt;:.'  <span class="hljs-comment"># Adds file to the root of the executable.</span>
</code></pre></div>

<ul>
<li><strong>File paths need to be updated to <code class="python hljs"><span class="hljs-string">'os.path.join(sys._MEIPASS, &lt;path&gt;)'</span></code>.</strong></li>
</ul>
<div><h3 id="basicscripttemplate">Basic Script Template</h3><pre><code class="python language-python hljs"><span class="hljs-comment">#!/usr/bin/env python3</span>
<span class="hljs-comment">#</span>
<span class="hljs-comment"># Usage: .py</span>
<span class="hljs-comment">#</span>

<span class="hljs-keyword">from</span> sys <span class="hljs-keyword">import</span> argv, exit
<span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> Counter, defaultdict, namedtuple
<span class="hljs-keyword">from</span> dataclasses <span class="hljs-keyword">import</span> make_dataclass
<span class="hljs-keyword">from</span> enum <span class="hljs-keyword">import</span> Enum
<span class="hljs-keyword">import</span> functools, itertools, operator <span class="hljs-keyword">as</span> op, re


<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">main</span><span class="hljs-params">()</span>:</span>
    <span class="hljs-keyword">pass</span>


<span class="hljs-comment">###</span>
<span class="hljs-comment">##  UTIL</span>
<span class="hljs-comment">#</span>

<span class="hljs-function"><span class="hljs-keyword">def</span> <span class="hljs-title">read_file</span><span class="hljs-params">(filename)</span>:</span>
    <span class="hljs-keyword">with</span> open(filename, encoding=<span class="hljs-string">'utf-8'</span>) <span class="hljs-keyword">as</span> file:
        <span class="hljs-keyword">return</span> file.readlines()


<span class="hljs-keyword">if</span> __name__ == <span class="hljs-string">'__main__'</span>:
    main()
</code></pre></div>

<div><h2 id="index"><a href="#index" name="index">#</a>Index</h2><ul><li><strong>Only available in <a href="https://transactions.sendowl.com/products/78175486/4422834F/view">PDF</a>.</strong></li>
<li><strong>Ctrl+F / ⌘F is usually sufficient.</strong></li>
<li><strong>Searching <code class="python hljs"><span class="hljs-string">'#&lt;title&gt;'</span></code> will limit the search to the titles.</strong></li>
</ul></div>
 

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    <aside>November 25, 2020</aside>
    <a href="../" rel="author">Jure Šorn</a>
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